Tektronix Type 575 curve tracer : repair and restoration

[Vince]

Hello World,

At last I managed to grab a 575 curve tracer. Wanted one so badly ever since I started getting into old glowing Tek scopes, 4 years ago or something. However too rare (one pops up every year or two) and way too pricey for me (500 Euros usually...). But what do you know, this one popped up at only 100 Euros ! As always good deals disappears within minutes literally, and since I saw this one 3 hours after the ad went on-line, I was toast... but tried my luck anyway, immediately offering 50% more to the seller, 150 Euros... he phoned me saying I was the highest "bidder", and the deal was done ! Next day he had another old guy happy to offer him 500 to steal it from me, but luckily the seller was honest enough to refuse the offer, and sticked with me, phew that was close ! 
Spent another 150 in petrol and tolls as the thing was 450kms away from me ! But either you are motivated or you aren't !    At 300 Euros once back home, it's still well worth it. And I can just pretend I was nearby to visit some friend or family or whatever... so as far as I am concerned it cost me only 150 

Anyway, so happy to have a 575, I am over the moon. Definitely the master piece in my collection of glowing Tek boat anchors.

Not only was it cheap, but it also comes with many hours of fun to restore it !
Indeed this poor 575 is in need of an incredible amount of TLC... so many things wrong with it.
However it basically "works" and there are no show stoppers, blown transformer or defective CRT... nothing of the sort, which is the most important !

I guess I could keep it for parts and look for another one in better condition, but they are too rare and expensive that I might as well wait for years and pay 500 for the next unit... nope.

So it time wise, or financially-wise... it's much cheaper and faster to just try to resurrect this one.
I am no magician so it will never be in concourse condition, but neither is my goal so that's fine.
Goal is to make it perfect electrically, make it a usable instrument, calibrated, accurate, as it should, and tackle the numerous mechanical and cosmetic issues as best I can. However I intend to take all my time and do the best job possible.

It's the basic 200 Volts version not the 400V one, but hey you can't have it all. That doesn't keep me from loving it to bits.

I have powered it up for an entire day, playing with it extensively, and discovered en route its numerous problems.

So I am creating this thread now, so as to log all the problems that need to be addressed, while I still remember them.. but probably won't have time to restore it immediately as so many other priorities currently, but I am really eager to start on it so am hoping it will see some action in the coming months.

Due to the varied nature of the problems that need fixing, and the sheer amount of them... what I am thinking is that the restoration will not be linear. I will probably look for the low hanging fruits first, that require little disassemby of the unit, as well as fixing the electrical side of things, then only move on to the nuts and bolt restoration to tackle the cosmetic side of things. Something like that...


Anyway, so let's list all its problems now.

E X T E R I O R

- Rusty screws all over, and on the metal work on the cabinet panel, carry handles.

- Carry handles need refreshing, looking sad as they always do. Looks leather buy looking more closely at the back of the  leather... I am not so sure ! Looks like fake leather fabric, I don't know...  Tek did make real leather handles (have some on my Type 317 scopes). Regardless, think I might redo them in real leather, possibly in black (type 317 had them black) rather then blue.

- RHS panel, top side, toward the front. The entire area between the front edge and the front of the little compartment that hold the owners booklet, is caved in. Doesn't show well on pictures, but it is...

- [ FIXED ] Door for aforementioned compartment: it is jammed closed. Only way to open it is to pry it    Problem I think is that it's misaligned, it's crooked. One edge of the door is hitting the panel. Don't know why just now. Given the panel is caved in in this area, I guess the instrument took a big hit that might have distorted the hinge for the door. Anyway, it needs some metal work to straighten things out...

- [ FIXED ] - Bottom right corner of the test panel (where you shove the transistor under test) is bent outwards, corner is sticking out, also causing the binding post present here, to be misaligned wrt to its two brothers above him. Panel seems to be soft aluminium so should not be too difficult to straighten.

- CRT bezel: bottom right stud is missing. This is one is no quick fix as it requires to take the entire face plate off !    So this will be done towards the end of the process, when I do the nuts and bolt restoration.

- [ FIXED ] - Knobs: the one used for the " Series Resistor " setting, in the "Base Step Generator " section of the front panel... is not the correct one ! Basic shape/ style is correct, but the colour is wrong, it's dark grey instead of black. Also it has a hole in the center as if it was meant to carry a secondary red know atop of it.

- " Steps / Sec " Toggle switch: its bat is bent, along two axis. Nothing dramatic but one you know about it it bothers you no end !
Not sure how feasible ti is to straighten it... too tiny to grad it firmly I think. Might be easier to just replace it, if I can find one somewhere...

- Corrosion and crustiness on and around and under all the washers and locking nuts for all the toggle switches and push-buttons. Looks horrible.

I N T E R I O R

- [ FIXED ] - Chassis, top, right side : missing the long stiffener/beam that runs from the front to the back of the instrument.

- [ FIXED ] - Chassis, left side, between back panel and lower deck : missing one of the three screws that secure the triangular stiffener.

- Chassis, left side, lower deck: missing a large panel with lots of printing on it, that covers the area where the rectifiers and collector voltage power stuff is located. Including a picture taken fro Tekwiki that show what this panel looked like... hoping I reproduce this panel.

- [ FIXED ] - CRT: its neck is completely lose, the mechanism that's responsible for rotating the CRT / neck is in bits. Looking at the exploded views in the service manual, I am missing the piece that grabs the neck. Well apparently it may not be "missing" but "only" disintegrated. Apparently it's a know / recurrent problem on these old Tek machines. This part was made of some rubbery lie material that disintegrates over time. As a result the neck is lose and it is therefore impossible to orientate the CRT properly. Luckily it seems like standard part common to all 500 scopes, not just the curve tracer, so I should be able to pinch this part from one of my 500 scopes. If not, I gather someone in Germany makes these parts, so I should be covered...

- Upper deck, center line, rear. There is a vertical piece of aluminium where a couple Germanium power trannies are mounted, kinda serves as a heatsink. There a few rubber grommets running through that heatsink. They look bad and some are missing. Well, the split in two and both halves migrated down the wire. They look kinda generic so hoping one can still buy them new today.

- These two Germanium transistors look rather crusty... hoping the oxidation has not migrated inside the case... however did a quick search and believe it or not these ancient trannies are still available, not new of course, but old stock.

- Cooling fan : slow to start and a bit noisy. Needs lubricating of course but from similar experience on my type 317, the slow start maybe caused by something more subtle that's not as obvious... I still have not managed to fi xthe slow start issue on this bloody 317 ! 


E L E C T R I C A L

- Wafer switch, setting range for collector voltage (either 0-20V or 0 to 200V). Huge damage to the outer most wafer, as obviously that's the most accessible. Luckily it broke " cleanly ", just one big chunk, not small debris. Also the broken part is still with us as it is held in the vicinity by wires that were soldered to it, phew.

- Toggle switch : " Mode " switch for the Base Step Generator. Has 3 positions : OFF, " Single " and " Repetitive ". The latter is what you want 99,999% of the time. Sadly if you flip the switch to this position, it won't stay there, doesn't lock into place, the bat immediately falls back down to the " OFF " position. The tip (in contact with the bat) of the corresponding moving contact in the switch, is broken, metal fatigue. In the pictures below you can see the tip of the contact massively bent, begging for life. Hanging in there with just a few iron atoms... I barely touched it and it snapped right off. I kept the broken bit just in case I manage to solder it back into place, or to use as a template to replace this contact using another contact from god knows what apparatus. An old beefy relay of some kind.  I think it's not a lost cause, but still not a quick and easy fix.

- Power socket : the instrument still has its original USA style socket. However a modern European power cord was also fitted, for convenience. Problem is, guy who did it did very poor job, a dangerous one even. He soldered the wires from the cord, straight to the terminals at the back of the original socket... the quality of the solder joints leave a lot to be desired !  Also, the insulation of the blue wire has a big cut in it, exposed copper ! And to top it all... guy didn't seem to believe it was worth connecting the earth wire at all !    So all that needs redoing properly.  Might get rid of the cord, remove the USA socket and replace it with a modern IEC socket, as it's more practical. I hate instruments with hardwired power cords (or whatever cord at the back of the unit), they drive me nuts.

- [ FIXED ] - Now on to actually testing the operation of the 575, with a transistor plugged in. I can display a set of curves, however they look weird. Other than the obvious orientation problem because of the loose CRT, what bothers me is the lack of vertical line on the left, joining all the curves... i.e. the linear region of the transistors. It's just not there at all ?!      All I see are the horizontal / saturated parts of the curves. On their left all I see are curled wiggly lines connecting the left edge of each curve together ?!     Definitely not right..


OK I think that's about it as far as problems go. Did it from the top of my head but I think it's a complete list... well of course I may well discover more problems later on, as I work on it... but that's all I noticed in this "first pass" so to speak.

Now for the pics illustrating all that, hopefully in a similar order to the text, to make it easier to follow...

[Vince]

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[Vince]

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[Vince]

Oh boy, I was so focused on describing everything that's wrong with it, that I forgot to post some pics of the thing, sorry ! 

Here it is ! 

[Vince]

...

[Vince]

Instrument upside down, view of the tubes on the bottom side of the upper deck, and view of the bottom of the instrument.

And last, playing with a diode.

[Vince]

OK so the day I test drove the thing, I tried some quick things in the electrical department, before buttoning it up and putting it aside.

- Broken wafer switch for the Collector Voltage range selection : Since the broken chunk was still there and it broke cleanly... I mated it to the switch and it was a perfect fit, no gaps at all, wonderful. So I tried superglue-ing it ... thinking who are you kidding Vince... but much to my surprise it seems to hold up just fine ! I can operate the switch and the broken bit appears to stay firmly in place, it works !    Well at least it's good enough to carry on fixing the instrument, will se later for a better/more permanent fix.

- Broke, Toggle " MODE " switch. Stuck to the " OFF " position which is not very helpful is it... so I hard wired the switch to the " AUTO "position, so that at least the thing can actually run and I can use it and troubleshoot it ! Again will see later for a proper fix !

Once that was done, I could at least now get the thing to run so I could start trouble shooting it...

I don't have a tube tester so I did what has already worked for me once.... simple things !  I turned the lab light off, and looked closely at all the tubes. I noticed that one of them was not glowing at all, not even very faintly. So I pulled it and replaced it with a used one salvaged from one of my Tek scopes. I have a crusty type 531A that I use as a donor.

Tube in question was V132 a 6AL5, it's a double diode. According to the schematic it's directly tied to the STEPS / SEC toggle switch of the Base Ste p Generator.

With a replacement tube, things improve quite a bit : I can now at last see the vertical line representing the linear region of the transistor ! At last it looks like what I saw in text books 25 years ago when I was studying EE ! 
So quite happy.

However that came with a new problem : the display is now not clean, it's very unstable / fuzzy. like the curves never get redrawn exactly at the same spot. See pic below.

Given the age of the thing, before doing any electrical troubleshooting, first thing is to care for dodgy contacts... so I spent an hour and half flooding the instrument with half a can of precious " Deoxit "  contact cleaner. Exercised all the switches, toggle and wafer types alike. Pulled each and every tube, poured some Deoxit in the sockets, put the tubes back in while "exercising" them for 30 seconds in their socket, to break the oxidation layer on the tube pins and sockets.

That did not make the slightest of difference sadly 
But well, it had to be done first. Now I know the unstable picture is more likely to be an actual electrical problem, which I can now start chasing.
Could still be a bad connection somewhere, but something else than switches and tube sockets.  Could be an intermittent connection in a component, capacitor or resistor, internally, where the leads bond.
Could be a dodgy solder joint on a switch or ceramic strip. 
Could be a dodgy tube as well ! An intermittent internal bond between some pin and the metallic structure it connects to.
Hell I guess that should be my first take on it, seeing as BEFORE replacing the tube, the display was STABLE...
Yeah, I will just try another tube to see if that changes anything...

Another problem : I get some weird stuff going on, as you can see, toward the right tip of the curves. A squiggly line that connects the curves together. It's perfectly repeatable, always the same shape... so to me it's unlikely to be a bad connection, it's rather some very deterministic electrical issue somewhere. Looks like a "retrace" issue on an old CRT monitor or something !     I must add that it shows only when the STEP / SEC switch is set to 240. That's where I took the pics below.
At the slower 120 steps/sec setting, no squiggly lines. Or maybe there is but it's fainter and I can't distinguish it, who knows. Thought it was worth mentioning as that might be a clue in its own right...

Oh, and last "problem".. well not really a problem, nothing is broken... is that the horizontal amplifier is all over the shop : trace moves widely, going off screen often, as you change caliber. So it's impossible to make any measurement whatsoever as you just can't trust whatever is on screen... No big deal though. Had a similar problem with my type 317. IIRC the " DC Balance gain" control is there precisely to fix this problem ! so will adjust that and of course recalibrate the amplifier at large. I want to be able to use the instrument, not just display vague shapes on the screen for fun... even it IS fun in itself ! 

OK so that's were I am at with this thing... don't know when I will find time to put it back on the bench...

[xrunner]

Thanks for this thread Vince. I've been following what you've done on this in the TEA thread, but it's a very good idea to make a dedicated thread for this. I'll be following.

[Johnny10]

 

I've got three 575's. 1-200Volt, 2- 400 volt.
One of the 400 volt units came in mint condition so I put it back in the box 4 years ago and haven't touched it since. :-).

My 200 volt version is a bit rough but working. Had the same CRT yoke deterioration as yours.

I haven't opened any of them in a few years.

I use the 576 more than the 575's.

Good luck with yours.

[Smoky]

Good luck with your project Vince

I'd love to find a 575 in mint shape cosmetically

What I did to a little 310 oscilloscope, I'd do to a 575!

[BU508A]

Following, just because of the glowing tubes. 

[Johnny10]

I really like the red grid in these units!

[Greybeard]

Congratulations for grabbing a 575!
But that 575 was looking really ugly.
What has happened to it?

Harakiri wiring...

[Johnny10]

He got a bodged unit.

But here in the states we have so much more available.

I paid 50 for my rough 200 Volt unit and 130 shipping.
I think the mint unit cost me 375 total.

[Vince]

Hi people, thanks for your interest ! 

However I fear you will all quickly lose interest if like me the forum FAILS to send you bloody e-mail notifications when something is posted ! 
Has been broken for me for the past 2 or 3 days !

Yep I got a bodged one. Forgot to talk about it but the seller told me he had too bad units and made this working one out of the two.
Clearly he is not very handy and lacks attention to detail....

But as I said I can't be choosy ! It's frog land here, not the US/ Tek's home land.... any old glowing Tek stuff is hard to come by and the 575 is a rarity among the rarities ! Only one comes up every year or two or three ! And usually at hundreds of Euros, like 500 or something. And even if I had 500 Euros to spend on one, which I have do not, it still does not mean I would be able to have it, as there are a million people here who want one, competition is fierce, and they get sold literally withing the first 20 minutes going online on our local web site !!!  Plus it's too big and heavy to be shipped, so even if you find one for 500 Euros, you may well have to spend another 500 or 600 to drive to the other end of the country and back, to bring it home ! 1000 euros total, can NOT do that !

So really, getting this one for only 150 Euros, 150 more to travel to pick it up... it's still a miracle, regardless of its horrible condition and basic 200Volts spec !

Plus, there is so much to do to fix it up, that by the time I am done it will have created a strong bond between me and hits puppy. I will feel at one with it. I will feel worthy and deserving of it too, because I will have put so much work into it to bring it back to its former glory !

I find this much more satisfying and fun than just putting 500 or 1000 euros no the table to get a NIB one that needs nothing done to it whatsoever.

Main point as I said is... there is nothing fundamentally wrong with this unit, I didn't waste my money far from that. It's complete, all the tubes are still in it, all the vital unobtainium parts are in good health (CRT, transformer...), and it basically works out ot the box.  All it needs is some TLC ! A lot of TLC, really a lot.. but still TLC only ! So there no reason why I should not be able to make this 575 work just right, and look 10 times better than it does now... this puppy is just crying out for love and attention, and I am here to give it just that ! 

[Johnny10]

I'm not losing interest, if you look at my signature line you will see I am a curve tracer fanatic.!

I've bought many 576 units which I repaired and sold.

Love them! Do I need one? Doesn't matter.

I even bought a non functioning Keithley SCS4200 last year which I will patiently wait for the parts I need to show up.

More power to you Vince. Live your Dream.

 

[Vince]

Oh OK... looks like I didn't need to worry. Talked about it on TEA... appears that e-mail notifications are not broken for everyone... just for me.. plus I now understand most people do not use em-ail notifications anyway, they rather actively poll the forum all the time for new messages... well in this case people will be able to see what' going on here, good !   

... still, I need e-mail notification fixed, I use only that... please someone fix the notifications on this forum ! There offer a 100 Euro bounty ! 

even bought a non functioning Keithley SCS4200 last year which I will patiently wait for the parts I need to show up.

Wow, checked this on Google... looks like a trillion dollar bit of kit ?!   
You got a broken one for super cheap ? Even super cheap for such an instrument must be like 5 grand or so 

I hope you can fix it, people will make appointments and pay you 10 bucks a minute to be able to use your gear ! 

[SoundTech-LG]

Vince!

Looks like you nabbed a REAL boat anchor!!!    Just kidding, but maybe it was used shipboard??? At the very least on the beach, or dock.
The good part is those handles! They are perfect compared to the ones on mine. My handles have a thin strip of `rusty metal left to grab onto...  bloody dangerous.
I have the disintegrated neck clamp too. Mine seems to work well. Dusted and cleaned everything up inside. The selenium rectumfryers worry me though. Might have to do the silicon mod.
Have fun... you'll be happy when it's done. Like you always wanted one for 40 years or so. Now what to do with it???

[KE5FX]

Looks like a nice restoration project!  I'd probably replace those germanium power transistors sooner rather than later.  They get leaky with age.  When used as series pass elements, the supply voltage ends up too high due to lack of control margin, which might stress some other parts that are hard(er) to replace.

[Vince]

Vince!

Looks like you nabbed a REAL boat anchor!!!    Just kidding, but maybe it was used shipboard??? At the very least on the beach, or dock.
The good part is those handles! They are perfect compared to the ones on mine. My handles have a thin strip of `rusty metal left to grab onto...  bloody dangerous.
I have the disintegrated neck clamp too. Mine seems to work well. Dusted and cleaned everything up inside. The selenium rectumfryers worry me though. Might have to do the silicon mod.
Have fun... you'll be happy when it's done. Like you always wanted one for 40 years or so. Now what to do with it???

Have no idea what kind of life the two donor he used had...  all I know is what kind of life they WILL have with me now, a much better life for sure ! 

The Selenium rectifiers, well have no experience / much knowledge about them... but saw a short video about them earlier this week. Apparently even back in the day they used fail quite often, producing a horrible smell...

As to what I will do with the 575 once it's done well.. I intend to build a nice cart to put it on, so I can wheel it around the lab and use it as often I can find an excuse to ! Like testing zener diodes, and also testing vacuum tubes on it (using some simple external circuitry in a custom test fixture) to help me restore my 20 or so glowing Tek scopes. I guess I could just as well test FET transistors on it, DIACs....

Basically give it a full time spot in the lab where it can be seen and enjoyed, and find any excuse/pretext to fire it up ! 

[Vince]

Looks like a nice restoration project!  I'd probably replace those germanium power transistors sooner rather than later.  They get leaky with age.  When used as series pass elements, the supply voltage ends up too high due to lack of control margin, which might stress some other parts that are hard(er) to replace.

Thanks for the warning. I have not looked at the schematic so I don't know what part of the instrument these two Germanium trannies are used in. Given their location in the unit, I would guess they are not part of the power supply, but rather must have to do with the supply of the Collector voltage applied to the DUT.

Will check the schematics to see what kind of DC levels theses trannies are supposed to experience, and probe them to see how far off they are...

When you say replacing, do you mean getting NOS ones (as seem to still be available) or replace them with modern silicon trannies ? If so have people figured out a substitute and have experience using them ?

[SoundTech-LG]

Yeah Vince,

The Selenium smells bad, but is highly toxic as well. The only remnant of my 555 is the cart I had for it, now the 575 sits on it. If I just had room to roll it around!!! 

[KE5FX]

When you say replacing, do you mean getting NOS ones (as seem to still be available) or replace them with modern silicon trannies ? If so have people figured out a substitute and have experience using them ?

I'd look for silicon parts with similar power dissipation, Vce and fT ratings.  Assuming these are germanium parts, you can bet that if good silicon power transistors had been available at the time, they would have been used instead. 

If they aren't series-pass regulators, though, you're probably fine waiting to replace them.  Take a look at the circuit and ask yourself, "What's the worst thing that could happen if I put a resistor between the emitter and collector?"

[Robert763]

Good on you for saving this beast.
Now you have had a quick play Id start checking all the powersupply rails for voltage and ripple. I don't advocate shotgun capacitor replacement, but you are likely to have some dodgy electrolytics.

[bd139]

Consider me subscribing to this thread. Good luck and fingers crossed for you.

[med6753]

Following too.

[factory]

Yeah Vince,

The Selenium smells bad, but is highly toxic as well. The only remnant of my 555 is the cart I had for it, now the 575 sits on it. If I just had room to roll it around!!! 

I'm a little surprised the Tek diode modification doesn't use any dropper resistors, particularly for the +100V supply, as the pass tube will be dropping the excess voltage from the more efficient silicon diodes, then again they were probably adequately rated (other TE such as PSU's may need further modification, to avoid exceeding maximum voltage ratings of pass components).

I would have thought TE manufacturers would have used parts with decent ratings (unlike TV/radios where lower cost/rated parts might be used), plus the Tek 575 seems to have decent forced air cooling for them too (unlike those used in industrial, crane* & lift/elevator etc. control boxes which might only be passively cooled), the low voltage diodes also have fuses fitted before them, which should prevent overheating from a shorted smoothing capacitor.

*I remember maintenance bringing a rectifier for a crane brake to me several times over a few years, to replace the shorted silicon bridge, to me it looked to have originally had a metal or selenium rectifier.

Selenium rectifiers & suppressors are still available from GD rectifiers, they can't be the only supplier.
https://www.gdrectifiers.co.uk/products/category/power_assemblies/selenium_rectifiers/
https://www.gdrectifiers.co.uk/products/category/power_assemblies/selenium_suppressors/

Personally I have lots of test gear with Selenium diodes and no plans to replace them unless they fail, which could be due to overload from shorted capacitors, or the voltage drop increasing with age, YMMV.

It would be interesting to hear about any Selenium diodes in old test gear (not TV or radio) that have failed with smoke being released, just can't seem to find anything with a quick search.

David

[Vince]

Thanks chaps ! 


@Robert : power supplies all good.

-150V (reference rail) : -149,0V ripple 2mV on AVG DMM (so 6mVpp or so ?)
+100V : +98.8V  ripple 3mV AVG, <10mVpp
+300V : +298,9V ripple 4mV AVG so 12mVpp or something I guess.

Have not dared looking at the ripple on my scope (no diff probe here nor isolation transformer beefy enough), even though when you think of it, the Tek having a linear supply, its transformer is actually isolating the scope, doesn't it... and its earth pin isn't even connected..

Still, I am paranoid so I didn't scope it.

It's worth mentioning how thoughtful Tek was wrt to testing the power rails : on a 500 scope there are no test points. You need to tilt the scope on its side, remove the bottom cover, and probe directly on ceramic strips, on fully exposed circuitry... better watch your fingers and not slip your probe, or it could ruin your day and/or that of the scope !

But... on the 575 it's much easier and safer : you can leave the instrument upright in its normal position. Just pop the RHS cover and you have 3 test points right there, laid on the side/edge of the lower deck, conveniently labeled as well. Test points are well insulated / safe.. it's hard to screw up when doing the measurements ! A delight....

@ Factory : Wow incredible that one can still get these old fashioned Selenium rectifiers, good to know ! Who knows maybe one day some tiny fab in china will start making obsolete Germanium trannies as well ! 

BUT .... BUT !!   What do you know... I checked the service manual and this Selenium looking unit is apparently GERMANIUM not Selenium !  6 cells, rated 0.5A / 300V each. So maybe they are more reliable and don't smell crap and intoxicate you with their fumes.  I will therefore leave them well alone since they work fine right now. Also... they are NOT used to rectify the main power supply.... no. They use it to rectify the Collector voltage !


- The two crusty power Germanium transistors : looked them up in the schematics (see attached). They have an easy life, not going to burst into flames any time soon ! I mean.. they have nothing to do with the power stuff associated with the collector voltage/current....nope. These two Germanium trannies, as beefy as they look, are tied together in a Darlington kind of way, and see only 28Volts, and current wise they only supply the BASE current for the DUT !
So not too worried about them, and even if they do go the instrument will not catch fire...

- Good news : I managed to FIX something !     When I removed the RHS cover panel, I looked more closely at the compartment at the top, wrt to the door being stuck closed. I noticed the hinge (a simple metal rod) was sticking out quite a bit on the visible side, like 8mm or so. Looked a little suspicious to me. I tried to push on it with my finger to see if it would budge... it did ! It went back into place... then all by magic the door alignment corrected itself, and now the door can be closed and opened just fine, every time, never misses  a beat ! One problem fixed !

I updated my original introductory post in the thread to reflect that... all the problems are listed there quite tidily, so I think it's quite practical to just go back there to update it anytime I manage to fix something. Makes it easy to see how the restoration is progressing.

This compartment is also MUCH deeper/bigger than its counterparts in 500 scopes (where it's super shallow and you can not fit anything more than the booklet it's intended to host), because well... there is less stuff to cram in the instrument.
It's actually large enough to host a set of probes I think ! Too bad it's not a scope, doesn't need probes ! 
Oh well, I guess you can use it to store some bacon to keep it warm... 


Spent a few hours playing with the thing to work on the trace instability issue. I think I got somewhere. Didn't find the root cause of the problem so no fix, but I gathered lots of interesting clues which is a good start...

1) Took a wooden stick, and tapped on all of the tubes, every component on every ceramic strip, tapped on all the power components on the LHS where the collector stuff is. Did the same underneath the instrument as well (flipped it on its side). Even tapped on the CRT where the deflection plates terminals exit the glass tube. Also tapped on the big connector at the back of the CRT... then wiggled the wiring harness connected to it... then its parent harness...

Result : NADA ! Not a sausage !   

2) Played with the controls / knobs, to see if there were dirty even though I had already given them a good shot of Deoxit the other day... still nothing. Not a dirty switch issue.

3) Gave the top and bottom decks a good shag... nothing.

The instability remains there, perfectly unchanged, no matter how I torture the instrument.

Kinda disappointed.... no easy fix for Vince !

So then tried the next approach : tried using the instrument, playing with all the knobs, trying different things to see if I could make the instability go away, or at least discern a pattern at some point.

That's where I made progress ! Again no fix just yet, but still some progress I think !    I will let you judge of that...

In short :

1) The instability remains NO MATTER WHAT

2) It is present on both X and Y axis.

3) Its amplitude remains unchanged REGARDLESS of X and Y amplifier setting/sensitivity. The  instability spans about 2 small graticule divisions on the X axis, and a bit more, almost 3 divisions on the Y axis.

4) Is present whether I test a transistor or a diode. That is, whether you make use of the Base Step Generator or not, hence one can rule out the entire Base Step Generator subsystem, I think...

5) It is present with or withOUT a DUT present ! That is, you connect nothing, you get just a flat line on the screen, zero current to be measured, hence should have zero "crap"/instability on the Y axis... yet you STILL get crap on the Y axis...somehow.


Then I managed to find a pattern at last : I tested a Zener diode, so that I can display a sharp "knee" on the screen. This gives me a clean horizontal and vertical trace on the screen, that I can use as a " test pattern " to observe what the display is doing exactly, on each axis.
That was a good idea... I made a short video illustrating this :




What this shows is that the "span"/width of the unstable area of the trace, varies depending on WHERE it is located on the CRT !
Weird.
It does so similarly on both axis, it's symmetrical left / right and top / bottom.

Basically, it is most unstable on the outer part of the CRT, that's where you get the 2 or 3 division span. Then as the trace gets closer to the center of the CRT, the extra/unwanted/random crap/traces, progressively get closer to one another, and toward the center of the CRT they kinda "merge" and give you the illusion of a solid (hence stable) line, albeit a very thick line.

The video illustrates this :

1) I start with the trace centered on screen : the vertical part of the trace is centered, so is the horizontal part. You can see the trace looks thick but stable.

2) Then I move the trace vertically, downward. You can see the trace become more and more unstable as I get closer and closer to the bottom of the CRT.

3) Then I move the trace to the top of the CRT and you can see it acts similarly, it's symmetrical.

4) Then I center the trace and this time move it horizontally, left to right, and you can see a similar behaviour.


So ... it's weird, but at least I have now a pattern that's perfectly reproducible, like Swiss clock work, so I have something to chew !
So looks like it's to do with the high-level stuff so to speak. Does not matter what you test or even don't test with the instrument, does not matter how you twiddle the amplifier knobs or collector voltage/current settings, or base step generator.... it's above all that, it's common to all of these things...

That rings " power supply issue "... but they are fine.

So something else... The CRT itself looks fine...  so something in between... final drivers for the CRT plates... but it's weird that it would affect both X and Y at the same time... so it should be something common to both X and Y display... pfffffff..... I really don't know.  Need to study the service manual, theory of operation, overall block diagram, schematics, hoping to get a bright idea some day...

[Vince]

Forgot... I turned  the thing off... then an hour later went to turn it back on... and it would not ! Dead as a dodo !

Blown fuse.... looked really crusty, and was not the appropriate one ! Read 1.6A fast blow. Should be 2A slow blow...   all the big 500 Scopes have a similar fuse, so I had already a 10 pack of those in stock, yeah ! Popped a new fuse, back to life ! 

So the fuse was not the right one, this was yet another problem I had not listed... but now FIXED ! 
One less problem on this bad boy ! Will get there one small step at a time, but I will get there

[xrunner]

Forgot... I turned  the thing off... then an hour later went to turn it back on... and it would not ! Dead as a dodo !

Blown fuse.... looked really crusty, and was not the appropriate one ! Read 1.6A fast blow. Should be 2A slow blow...   all the big 500 Scopes have a similar fuse, so I had already a 10 pack of those in stock, yeah ! Popped a new fuse, back to life ! 

So the fuse was not the right one, this was yet another problem I had not listed... but now FIXED ! 
One less problem on this bad boy ! Will get there one small step at a time, but I will get there

That's one small step for Vince - One giant leap for Tektronixkind. 

[Vince]

OK, already another update ! Could not sleep so been burning the midnight oil working on the thing, investigating further this trace instability issue.

To be 100% sure it was not the CRT subsystem at fault, I decided to do a quick test to rule it out, as there is something one can do easily... At the CRT glass, I unplugged the 4 wires for the deflections plates, so I can drive them myself, manually so to speak.
This way I could see if the instability would go away or not.

I connected one set of plates to my sig gen so as to be able to sweep the beam, and draw a straight line across the display. Then I could use my lab power supply to drive the vertical plates to make the line go up and down, and see whether the trace would become unstable as I move away from the center of the CRT. That was the plan...

At first I connected the sig gen to the horizontal plates so as to draw a horizontal line, seems more natural to me, somehow. However even when cranking my sig gen full blast, i.e. 20Vpp... that would produce a deflection / trace length of only 1.5 DIV or so !     Not very usable for my purpose here. So instead I connected the sig gen to the vertical plates, as it turns out they are a bit more sensitive. They would produce a deflection of 2.5 DIV or so.. still not great, but much better none the less.... so had to make do with that.
Then I connected my lab DC power supply to the horizontal plates. Twin floating 30V outputs. Put them in series so I can do 0 to 60Volts. Even 60V would give me only a 4 DIV deflection ! I need a high voltage adjustable supply I think...

The trace was extremely blurry, buried into a huge blob of noise. But, I could still discern the trace in all that noise, and could conduct my little experiment. The result was not what I had hoped.. at all.... the trace would STILL exhibit the same instability issue !!   

So... it means it does come from the CRT subsystem itself ! That explains everything, it's the easiest and most logical explanation I thought... but.... fuck me if the CRT is bad all is lost and it's the end of the restoration !! 

OR... I thought with some "luck", it could be due to the  CRT supporting circuitry, rather than CRT itself . I mean there is focus, astigmatism, geometry settings in the CRT gun, and all these things interact with each other and can produce weird and wonderful things on the CRT target...

So, I figured maybe a bad cap somewhere in the CRT circuitry... but for now, while I am here, let's just clean all the contacts as a first measure ! Yes it's the only contacts I had not yet cleaned, I admit... 
So I cleaned the pins and wire connectors  for the deflection plates. They look dark grey, as if they were oxidized... but not really. It kinda looks like it's their normal finish... still, just in case, I put some Deoxit in there and used a tiny/pen style wire brush.

Then I moved to the back of the CRT neck. Pulled the big round connector, Deoxit in there and on the pins on the CRT side. Brushed the pins. Exercised the connector a few times on the CRT pins to help the Deoxit work its way.

While I was in there with this area apart, I did some cleaning. Got rid of the ton of crusty debris trapped around the neck, bracket, nylon clamp etc... looked horrible. Used the tips of my fucked up cheap tweezers as a pick tool to dislodge every crusty bit in  every nook and cranny. Then a bit of cleaning with hot water/detergent in a spray bottle, a brush, kitchen towels..
Looks 10 times better than before. Much cleaner, no crusty debris all around the neck/clamp.. now looks much more appealing. Not as off-putting as it did.

See previous / original pics posted on the first page, to appreciate the change ! 

With all the crust removed you can better see all the parts of the mechanism so you better see what's going on and needs doing... clearly as I initially thought, the part that embraces the neck and rotates inside the metal bracket... is indeed not there, or not anymore. There just isn't anything in there. The neck is floating a quarter inch away from the metal bracket !   

So I am starting to think that maybe, since the seller did Frankenstein this unit from 2 units... maybe he just had no good part in either unit, so simply didn't put one in, simple as that !    Picture of the missing part, exploded view from the service manual.

So, once I had "refurbished" the CRT, I powered the unit and gave it a test ride : PROBLEM FIXED !!!!   

Stable trace now, left to right and top to bottom ! 

But after having worked on the CRT, of course the alignment was completely off, like... off by 45° or so ! Needless to say the picture looked a bit weird.... so before taking pics of my success... I grabbed a pair of pliers to grab the neck and rotate it while powered up. A bit stressful I must say... Got it almost perfectly lined up with the graticule... a bit more... a little bit more... allllmost there.... OH NO, trace is unstable again, and massively so, it's all over the shop, NOOOOOOOOOO !!!!!!! 

But I was not too worried, it was just proving the point. The problem was now most certainly due to a bad contact in the big neck connector. So I just moved the CRT a tiny bit and hey presto, picture perfectly stable again !    Played with the thing for 30 minutes, rock solid    PHEW !!!   

So the mystery is solved then.... I am glad it was that simple, no weird electrical bug to chase in the amplifiers or god knows what other part of the instrument !

A few pics to prove my success....

However I still have this problem with the squiggly lines towards the right end of the curves, that "jump" from one curve to the next. But it's a minor issue. Does need to be solved of course, but it's minor.  The instability issue was the real show stopper so I wanted that fixed or at least diagnosed, before I go any further with the restoration.

The squiggly lines however, whatever it is, I am sure is bound to be a minor problem which can be fixed any time in the restoration process, either before or after the full nuts and bolts cosmetic restoration.

For now, in the interest of making nice clean pictures, I made the squiggly lines go away by playing with the X amplifier controls, so as to make the squiggly lines go far away off screen, far away to the right.

Plus, I may have some clue about it. I noticed something interesting : the " STEPS / SEC " toggle switch. It has 3 positions :

120 / 240 / 120.

I.e 2 or 4 times the line frequency. Except of course in France / Europe it's 50Hz not 60Hz like in the USA, so I would get 100/200  refresh rates, not 120/240 !  Yet, the face plate of the instrument does say 120/240 not 100/200, even though it was not manufactured in the USA. Serial number does start with a 'zero' digit, not a 'B' (Beaverton / US plant). So I find this kinda lame from Tektronix ! 

Also, I don't understand why there are TWO positions marked " 120" ! There is nothing on the face plate that tells you what the difference between the two is ! Well maybe if I RTFM I would learn about it...

Anyway, the interesting thing is : the squiggly lines show up only in TWO of these 3 positions ! The 240 position, and only ONE of the two " 120 " positions !  Yes... somehow they don't behave 100% the same.
So that's great. I can now study the schematics and see how this working "120" setting differs from the other 120 and the 240.

So, I am making progress I think ! 

At any rate, now that the instability issue has been diagnosed and kinda fixed it seems, the unit now works well enough electrically, for me to be happy moving on with the restoration !!! 

[Vince]

Forgot to add : I looked a bit into that Selenium rectifier, and the silicon rectifier mod Tek offered.

I looked the latter up at the end of the service manual. My unit already has this mod implemented....

The big "Selenium" rectifier "stack" we see in the collector sweep area of the instrument, is nothing to do with the rectifier mod listed in the manual.
Indeed as the parts list pretends, although it does look like your typical Selenium rectifier, it is not. It is indeed Germanium not Selenium.

I looked it up. The part number printed on it is " GE4JA211CX278 " quite a mouthful eh ?!

The first two characters " GE " sound good eh ? Sounds like ... GE-rmanium ! 

Wanted to be 100% sure so googled it. ZERO hit ! However if you remove the last 5 characters and only consider " 4JA211 ".... then I found ONE hit.

OK to cut it short,  " GE " stands for " General Electrics " not " GE-rmanium ". Google found me the relevant page of a period GE product catalogue. They advertise this very rectifier.  "4JA211 " was the name of a series of rectifiers they made. Catalogue clearly states it's Germanium not Selenium, and it even shows a photograph of the rectifier, which matches 100% what's in my 575...

So there you go ! 

So no Silicon mod for me, it's already done. And no discarding the crappy / dangerous / ticking time bomb Selenium rectifier... as I don't have any in this unit !    So I will leave this Germanium rectifier stack well alone...

[Robert763]

Given the location in the circuit I would suggest that the Germainium rectifier was chosen because of the lower forward voltage drop compared to other technology available when the instrument was designed. A modern schottky diode might e siutable as a replacement. But.
"If it ain't broke, don't fix it"

[xrunner]

So, I figured maybe a bad cap somewhere in the CRT circuitry... but for now, while I am here, let's just clean all the contacts as a first measure ! Yes it's the only contacts I had not yet cleaned, I admit... 

Well I'm glad it's fixed but your killing me with this kind of suspense "Yes it's the only contacts I had not yet cleaned, I admit... "

 

But about that supporting collar. What is the temperature right there where it sits. I imagine it's hot but how hot? It can be designed for a 3D printer job but the material will have to be selected based on the temperature there,. i.e. PLA probably wouldn't work but there are others available ...

[Vince]

But about that supporting collar. What is the temperature right there where it sits. I imagine it's hot but how hot? It can be designed for a 3D printer job but the material will have to be selected based on the temperature there,. i.e. PLA probably wouldn't work but there are others available ...

Well I don't know I didn't put a temp probe in the thing while it was running !   Though that would be interesting I must say..... need to buy a temp sensor for my DMM first ! 

However no need to bother reinventing the wheel Martin.M  said a guy in his local forum, in Germany then, actually MAKES this very part already !  So I can just contact him.  However I don't even need to do that, no need spend any money : As I had hoped, I was able to salvage this part from my favorite donor, my crusty type 531A scope ! 
The part is made of hard plastic, that used to be clear plastic I assume... which is now heavily yellowed.... but it's still in perfect shape !
Maybe I could try " retro-brighting " it ?!  Worth a shot I suppose...

So that's what I have been doing today. Taking this part off of the 531A, which is a bit of a pain, then putting it on the 575. I was almost done then hit a brick wall : before I can put the CRT back in place, I need to tighten a bolt that secures the back of the CRT shield, to the metal bracket that holds the neck in place. But... that bolt goes through a little hollow spacer (see picture).. which I LOST !    When I took things apart, I heard it fall inside the scope, sure of that... it fell inside the scope not on the ground... searched on the ground anyway, no joy. Nowhere to be found in the scope either... I don't understand.... 

Maybe I will find it on the bench somewhere... some day. I can't pinch that spacer from the 531A because it is designed differently. Instead of having one single long screw going throughout a hollow spacer, what they did was use a threaded spacer, on both sides, with two tiny screws, one at the top one at the bottom of the spacer. So no good for me.

But luckily I think I can make a new spacer easily. My local hardware store sells anodized aluminium tubes that look exactly like what Tek used :

https://www.leroymerlin.fr/produits/quincaillerie/corde-chaine-cable-tole-fer-et-profile/fer-et-profile/profile-aluminium/tube-rond-aluminium-anodise-brillant-l-1-m-x-l-0-8-cm-x-h-0-8-cm-x-diam-8-mm-80108686.html

Well that's just an example. They have several sizes/diameters available so need to take measurements so I know what to buy once I get there... hopefully tomorrow (22H30 here, too late...).

While assembling the mechanism, I noticed that the white nylon clamp on the 575 is broken   
Luckily not in a show-stopping way, as you can see on the picture. The clamp part itself is intact, so it can grad the CRT neck just fine, that's the most important.
However as you can see the bottom part of the clamp, which holds the big nut you use to rotate the clamp... is cracked. Luckily this area is still strong enough to operate properly even with such a massive crack, phew !
I might try to repair it though....
I can't use the clamp from the 531A because it's broken too, but in a different place. It's the clamp part itself that's broken in two, so it's 100% unusable, scrap.

However... I could use this useless clamp to help me repair the one on my 575 ? I mean I could scrape some plastic material off of it to try to "weld"/fuse the crack in the 575 clamp ? Could also use it to practice welding on it, before I attempt a repair on the 575 clamp....
This way I could practice with the hot air station to figure out the optimum temperature to melt it. Hot enough to get a good bond, but not too hot that it deteriorates the plastic.

Yeah that could be a little project 

But for now it's gonna stay as it is, since it works... I will just make a new spacer real quick as it's really mandatory... but I will leave the eventual repair for the later stages of the restoration. For now, I am doing the first pass only : trying to figure out how I can fix things, try to see what parts I can salvage from others scopes... solve the big issues first. The fine tuning and polishing, that will be done later...

Anyway, I am happy I have this CRT assembly sorted out ! I am glad I have this 531A scope donor, would be screwed without it !  So next time someone asks me why I keep buying all these scopes.... well I need freaking PARTS at hand so I can restore those that can be saved and deserve to !
For example I have FIVE type 317 scopes ! Yet I have already restored one of them... so I don't need to keep the other four. Will I sell these 4 then ? NO WAY !!!     They are like little gold mines for parts of all kinds to save my bacon when restoring other scopes !

[med6753]

Why do you think I have a closet full of parts scopes ranging from a 2465 DMS to a Type 310A and several in between? Plus several 560/500/7000 series dead plug-in's. And at least 4 boxes/totes of additional parts. 

[Vince]

Good to know, if I need something I will PM you ! 

[Vince]

Worked a few hours on the thing again today. Making progress.


CRT
- Tried "retro-brighting" the plastic clamp for the neck, the part that I was missing. Didn't work at all, so I will have to get used to its massive yellowing.

- Lost spacer : went to the H/W store, bought a 8mm OD anodized aluminium tube and cut a new spacer, 8mm long. Used my tiny precision files made in China, to deburr the thing and make it look nice. Super happy with the result, looks like I bought one ! 

- put everything back together, reinstalled the CRT and gave it a test. I tested a Zener diode so as to display a test pattern that would give me a horizontal and vertical line as a reference. I played with the red knob of the clamp, to rotate the CRT, and it worked just fine. Te CRT is perfectly held in place, no wobbling around anymore, and I can easily fine tune the rotation. Had no trouble at all lining up the Zener diode pattern exactly to the graticule !   See pics.

KNOB REPLACEMENT
Big knob used to select the series resistor for the base of the transistor under test. Seller put an incorrect knob in there. Grey instead of black, and also with a big hole in the center, probably destined to host a secondary small red knob, I presume.

Once I had removed this horrible knob, I was in for a nasty surprise, see pic. Underneath the knob, 2 HUGE scratches, VERY deep!!!    Probably the guy didn't have the correct imperial size 1/16" Allen key so attacked the knob from under using a flat screw driver or something, and went crazy with it...     Problem is that even with the knob in place, you can still see a little bit of the scratches, it can't hide it all 

I replaced it with the proper knob, courtesy of my 531A donor as per usual.

Now come the good surprise : before, with the old knob I found it was behaving strangely: you could switch from the last position of the switch (highest base resistance, 22k ) to the first lowest resistance, 1 ohm) !! No stop ! I fond this crazy as one could easily by mistake blow the transistor under test in the blink of an eye ! I was bitching at Tektronix !
BUT... when I went to put the new knob in place, I had forgotten what position the old knob was in, so I reset the shat to put at one end. Screwed the new knob and.. hey presto, now you can't blow your tranny !  You can't switch carelessly from the highest to the lowest anymore ! Tek was not faulty, the old knob was imply not adjusted properly that's all ! Problem solved   
So the seller once again demonstrated his "talent"... destroys the face plate while taking the old knob out. Then can't even be bothered to put the correct knob and to top it all can't even be bothered to align the knob properly, meaning basically he had no clue what base resistor he was using as the knob was displaying garbage ! 
this guy blows my mind, really does !!! And he teaches electronics to engineers he said !! 

TEST PANEL
Well I call that the "Test panel" for lack of a better term... it's the "pod" at the bottom of the instrument that holds the sockets to fit the DUT. Well the bottom right corner of said panel is bent out of shape, it's sticking out. This also causes a binding post that so happens to live there, to consequently follow suit : it's not upright anymore, it's leaning a bit to the left, hence it no longer aligned with the other two binding posts above it. So I went to pull the panel out of the pod, hoping / thinking it would be easy and I could try to straighten the panel at my (mechanical) work bench.

Well it was not so easy...
There are four screw one can see from the outside, one in each corner.. I though OK let's just remove them and I can pull the panel. Nope. The top 2 screws you can remove. The bottom two you can loosen them but that's all, then they spin round, no luck. There is a nut behind the panel but it's not captive. Tilted the 575 on its side... oh there is a bottom cover one can remove. 3 screws. Then you get to see what's inside the pod, and you can remove  the two nuts. But the panel still won't move at all.
For that you need to free the switch : removed its big retaining nut from the outside. 16mm ( 5/8"), but need a deep socket so as to be able to clear the bat of the toggle switch. Standard socket no joy. So how do you do ? Well lucky me, I had a deep socket for the spark plugs on my car... it so happens to also be 16mm, how cool  ! 

So ow you can free the panel but... you can only lift it by a couple inches tops ! Because the bat of switch won't clear the panel, almost but not quite ! So the switch is keeping you prisoner !!!   So to pull the panel for good, one would have to desolder the very many wires going to the switch, which was way more than I had planned on doing, and way more than I could do this evening. So I tried to straighten the panel in situ ! Put a couple layers of masking tape on it to avoid marking it, then grabbed a pair of pliers and had a go at it, crossing fingers and proceeding with caution as you can imagine.
Well it went well. I managed to bend the corner of the panel into shape without making it look worse than it already was. It's spotless too, tape did its job.

Well to be honest I should have bent it a tiny little bit more... The corner of the panel looks good now, not sticking out any more, but the binding post is still sliggggggggghtly misaligned, just a hair. So I think later on I will probably have another at it. But I am splitting hair really. It looks fine. If you don't know what to look for, you would never see it I bet !
So overall very happy with the result.

ELECTRICAL
I just noticed that if you test a transistor, and if you look very closely at the CRT for the horizontal parts of the curves... then you see that lines are not "solid"... they show like a tiny ripple all over them ! OK  you say need to recap the power supply... maybe but as I said earlier, I have already tested the 3 main rails, -150/+100/+300 and they are all fine with very low ripple, it's within spec.

It does not do it when I test a diode... only with transistors.

I think I found the problem... think it's indeed a power supply, but not an obvious one.
As I had the 575 on i's side looking at the bottom of the test pod... my eyes inadvertently glimpsed at some canned caps, and noticed that two of them had a suspicious looking terminal ! See pic.  The positive terminal is covered in ... I don't kn,ow what. Looks like these caps leaked. Looked them up in the schematic, and then it all made sense : they are not part of the 3 main supplies I had already tested good. No. These 2 caps are part of a gang of 4 identical smoothing caps all in parallel : x4 2000uF caps, that filter... the power supply that supplies the base current for the transistor under test ! So yeah, I can understand how these faulty caps could forward their ripple to the screen, and why it would not affect diodes, since in this case, a dipole, you are not using the Base Step Generator so not using this power supply !

So... that's cool, looks like I may well be soon fixing yet another problem, and make the display on this puppy even more betterer as some would say ! 

I will replace all 4 of these caps I think, not just the 2 faulty ones. Not going to put crapacitors so I need to order online, so will cost an arm in shipping/minimum order, for 2 Euros worth of caps, pfff.... what wouldn't I do for my little 575...
Will have to buy some more stuff to meet the minimum order... but no more than that.

BTW, I pulled the condom off of one of these  cans, and it says 30th week of 1963. So mine is 58 years old !
Will probably be 60 by the time I am done restoring it....
Caps all rated at 20V.

CLEANING
Now that I fixed the test panel and knob.. thought it was about time to finish the job by giving the front of the instrument a good cleaning. Basic stuff, 30 minutes, no taking apart of anything, just some detergent with hot water in a spray bottle, a stiff tooth brush to clean all the crap on the knobs and every where... and off you go. 30 minutes later it now looks much better. Test panel is now so much more pleasing to look at ! Just compare before and after pics...

Now that it's clean I can see what defects / imperfections are left. Answer : all of them. That poor face plate is riddles with a myriad o very deep scratches, worn out spots, stains... it's hopeless, will have to leave with that. Again the poor 575 was in such a poor overall shape inside out the it was clear from day one that I could not do miracle and turn it into a concourse winner no matter how hard I try... it's worn out, can't fight that ! 
So the goal has alwyas been to make it look as good as possible, do everything that's reasonable, but that's about it.. I am no magician ! 

Anyway, I enjoy it much better already with what I fixed so far and this first pass at cleaning it, and anticipated the future improvement I will make to it's appearance as I go. So I think I can make it look quite decent and that will somewhat balance things out....

Test panel : as you can see, the paint is worn out / faded toward the left. I think because that's where people put their greasy fingers whenever they stick a tranny in the test socket. However, all is not lost ! I noticed that the artwork is NOT printed on the panel, as it is on the 500 scopes. No... look like Tek wanted to innovate with the curve tracer... all the artwork is actually engraved !    ALL of it... text, lines, symbols, absolutely everything. So basically I could fix the paintwork by just adding some more paint in the  "grooves", then wiping the excess and that's it ? Will need to experiment and ask around what kind of paint is best suited for that application. Need to have it custom mixed too, to get the colour right... so not something to improvise, but sounds doable eh ?!

Then I looked at the face plate.... you won't believe it.... they went wild and also engraved the face plate too ! ALL OF IT ! There is not a single thing that is printed on the face plate ! Even the Tektronix logo and accompanying text, it's all engraved !  wtf:
SO !!! That means that ONE DAY, when I am retired and have lots of time, and some money to spend... I COULD fix this 575 after all ! I could just sand down allll the scratches and blemishes and ever defect, make it 100% perfect. Then I would have to send it to some specialized company so they can re-anodize it just like Tek did. Then I can go wild with black/red/blue paint and redo all the artwork, then a couple coasts of lacquer to protect it all, again like Tek did... and hey presto, a brand new face plate !! 

I could also do the same all the chassis parts, most notable the lower deck, which are pitted/ corroded beyond recovery. Cleaning it will never make them look shiny and spotless again, forget it 
So here too, I could just sand them to removed every bit of pitting, then anodizing, then I will have to redo all the printing on it (vacuum tubes types and part number mostly), then lacquer. Brand new chassis.

But that's just a dream, it's well beyond the scope/ambition and budget of this restoration. But that's OK. Everything I do now, is something I won't have to do later on if I decide to have another go at the restoration one day.



Well overall it was quite a day for my 575 I think. Made quite some progress. fixed a few things, diagnosed some others, gave it a good clean, now looking much better.... yes it's a good day for him !


A few pics and off to bed, it's 7AM FFS ! 

[Vince]

..

[Vince]

Attached the schematic of the power supply, showing where are my two bad caps. So again it's the power supply that supplies current to drive the base of the transistor under test. It's not regulated, as simple as it can get : a few rectifiers, then followed by those 4 big 2000uF can caps in parallel. My 2 bad caps are two of these four.

[tautech]

TBH you'd be nuts not to replace the few extra PSU caps whilst you're in there. 

[med6753]

Agreed, take no prisoners. Replace them all, including the cans in the rest of the PSU.   

[xrunner]

Looking good Vince - long way to go.

[Vince]

No shotgunning here !  I am not in the US? I have no admiration for big weapons and mass shootings. I prefer finesse !   

The caps in the other power rials do their job just fine as is attested by the ripple that's within spec. Their job is to contain ripple. They do their job just fine, so by very definition, they are GOOD.  Have been good for 60 years, and you would like me to replace them for modern crap (no matter brand it is) that will last just a few years at best ? and might even die before the old one would have, had I let them in place ?! Silly ! 

These caps are going nowhere. I will replace them if and when necessary.

The only shot gunning I am will to do as I already is said, is to replace all 4 caps in the faulty power rail, rather than just the 2 bad ones.. because they are all in parallel, it's one entity. If 2 failed, maybe the other will soon, or are on their way already, don't know haven't checked. So it does make sense to replace all 4 at once, I fully agree with that.

But no more.

Get over it you mass shooters ! 


Trying to think of what I could do next on the 575, might have an idea or two. Stay tuned 


Oh BTW I checked all my old Tek scopes, and go figure, many of them DO have an engraved face plate too !  and I never noticed it thus far !!!

I am not sure why some are engraved and others are printed. It's not a price point problem I think, because some of my cheap/modest type 317 are engraved, yet the fancy super expensive type 547 and 549 are printed instead.
hell, I have even two scopes of the same type, two 515A... coming both from the sample plant ( code/prefix '1' ) one is engraved, the other is printed ! 

My best guess is that it's technological problem ? Maybe they sued engraving in the early years, then when printing became available they moved to that as it was probably cheaper / faster to produce ? If so, the S/N of my two 515A ought to reflect that. The S/N of the engraved one ought to older than that of the printed one... gonna check right now...

[med6753]

If you want to tempt Murphy and his capacitor goons then be my guest. Better to start with a "clean slate" rather than going back in again at a later date.

Kill them all. 

[Vince]

There is no reason to replace them early, no problem going back there later because in this 575 access to all htese caps is easy. I do not have to take anything apart to get to them. Whether I replace them this week or in 3 years makes absolutely no difference.

I do agree with your point though... you have to balance Murphy with the physical accessibility of the caps. In my 317 or a very crowded 547 or 549 or 545, it could well be that need to tear half the scope apart to get to the caps, in which case yes better to do it while you have the scope apart during its restoration.

But it's not the case in this 575. I just need to pop the covers off and the caps are all right there at my disposal.

Another good example would be a portable scope from the '70s. It's so tight in there, such a pain to take apart to get access to anything, that yes, once you have ti apart, you REALLY don't want to ever have to do it again ! 
So yes for this type of scopes, I too would replace all electrolytics, aluminium or dipped tantalums alike.

[Vince]

Just checked serial numbers on my two 515A. Seems to comfort my theory : the oldest of the two is the one that's engraved, newest is printed.

I might even be able to tell pretty accurately WHEN did this change occur, because it so happens that my two scopes have VERY close S/N !

100719 and 100800 ! 

So if I looked at date codes on the can caps, that would narrow it down pretty well.

[tautech]

If you want to tempt Murphy and his capacitor goons then be my guest. Better to start with a "clean slate" rather than going back in again at a later date.

Kill them all. 

Agree although Vince would be wise to at least measure the remaining 10 PSU caps to not only preempt their failure but also to protect the now days valuable glowing glass.
I do understand his resistance to yank those few big caps out and lose the originality of the design but there is always the option to repack the cans with new caps.

[Vince]

I am all for testing Tautech, as soon as I get my hands on an ESR tester ! 
So many things to buy, so little money !

[bd139]

Make one. I did  . Based on this excellent design: https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/

My attempt. Not pretty but it works: https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/msg2327025/#msg2327025

There's also an ESR adapter for DMMs here as well. I might build this as well as I have dropped my analogue one about 20 times recently and it's looking a bit bashed up now 

https://www.eevblog.com/forum/projects/esr-meter-adapter-design-and-construction/

[Johnny10]

I am sure you already have this Transistor Testing Manual but in case some others haven't seen it... I have found it very helpful.

https://worldradiohistory.com/BOOKSHELF-ARH/Technology-General/Tektronix-Some-Transistor-Measurements-Using-the-575-1959.pdf

[tautech]

I am all for testing Tautech, as soon as I get my hands on an ESR tester ! 
So many things to buy, so little money !

Low ESR is far less critical in linear PSU's and you can get by with just a capacitance meter where if measured values are 10+% from labelled values is a good signal to replace.
As you probably don't do any SMD work one of them $5 testers like BD posted will likely serve your needs.

Years back I splashed out on SMD Smart tweezers for such tasks and have never regretted it although they cost as much as a cheap scope these days yet so small they fit in your pocket.

[Vince]

I am sure you already have this Transistor Testing Manual but in case some others haven't seen it... I have found it very helpful.

https://worldradiohistory.com/BOOKSHELF-ARH/Technology-General/Tektronix-Some-Transistor-Measurements-Using-the-575-1959.pdf

Nope didn't have that, thanks for the link ! 

Much interesting, now downloaded and safe 

[Vince]

As you probably don't do any SMD work

Not sure what you mean ? Just 2 weeks ago I designed an SMD board and assembled 10 of them ? 

Years back I splashed out on SMD Smart tweezers for such tasks and have never regretted it although they cost as much as a cheap scope these days yet so small they fit in your pocket.

Oh yes, I remember a few years ago you trying to convince me to buy them ! When I looked at the price I ran away fast !

I am sure it fits your use case perfectly or else you would not rave about them so much, but for me as I don't spend 10 hours a day checking SMD devices, a DE5000 with the tweezers plugged in it will do just fine, more versatile, accurate and feature rich. Cheaper too !



Anyway, thanks BD for the links !

I like the analog meter design, but I don't have a meter movement at hand.
The second design / DMM adapter looks interesting in that it's compact and rugged, but I don't like the fact that the reading on the DMM is not direct, it's not 1:1.  10mV on the DMM means 100mohms ESR. it's awkward and error prone... and it necessitates a DMM, takes  more space on the bench, an extra set of test leads...  I prefer an all in one, integrated design, and direct reading.

I thought this through and I think in the end I will just get one of these very popular dirt cheap component testers from China :

https://www.ebay.fr/itm/263196467435

I need one of those to sort through my pile of salvaged semiconductors, so I can put them in boxes. Tester even has SMD pads so one can test SMD  SOT23/323 packages too, which is invaluable to me. These tiny packages have of course only cryptic markings on them, at best. Tester takes only a couple seconds to tell you what a random SOT23 package contains : single Zener diode (I did come across a SOT23 packaged Zener diode once !  ), double diode, BJT or FET, tells you if it's a NPN or PNP, even the pinout... for this alone it's well worth the 10 Euros it costs.
Since it also can measure ESR, then well, there you go, why buy a dedicated ESR meter...
Probably won't be super accurate but who gives a crap, it's only to check 50 year old filter caps ! I am not trying to LCR characterize some mega expensive fancy component off of the production line with a 6 digit 10,000 Euros Agilent precision LCR meter !

Hell even only 20% precision would still be more than enough to be able to make an informed decision about an old cap ! 

So I am gonna buy that I think.. probably in 5 minutes, decision is pretty much made at this point.

However for the fun of it, I still would like to make my own dedicated ESR meter, like the analog meter you made, retro style, with a nice wooden cabinet (I like fine woodworking so that would be an excuse to make something), with a flat black aluminium face plate, with an old meter movement, I like the very old ones which are round with a black painted metallic bezel, sitting flush. Don't like meters that protrude too much above the surface of the face plate.  So would need to salvage a round meter from some WW2 piece of TE... and make / print a custom scale for it, using a similar font to the original meter so as not to look out of place.
Yeah would love to do that at some point !

In the meantime, to get the job done quickly and cheaply... will get that 10 Euros do it all tester ! 

Will take at least 2 weeks to arrive here, but not a problem since I already know I am going to change those 4 caps anyway ! 
So gonna order the new caps right away and change them now, not gonna wait for the meter to arrive...

[Vince]

OK worked a bit on the thing, not much but what's done is done...

Fixed a couple items from the "mechanical" trouble-list...

1)

Added missing screw to the triangular stiffener, LHS, between lower deck and rear panel. Courtesy of the 531A as usual. Well to my dismay I didn't find the 100% correct screw, somehow. I mean it's the same shape, head, dimensions etc, but the surface finish on the head is slightly looking yellowing if you pay attention (visible on the pic too). It's very slight, but enough for your brain to notice something's "off".
Not that pronounced so I won't lose sleep over it, but I would still like to find a screw with the proper finish. I guess I will just have to visit one of my other scopes... bummer. Trying to take as many parts off of the 531A and leave the other scopes alone, but I don't think I will have a choice here.
Anyway, it's much better than with a missing screw, so am happy with it for now 

2)

The missing beam / stiffener, top right of the cabinet, that goes from the panel all the way to the back. I was about to salvage it from the 531A. However it would not fit as is, because the cabinet of the 575 is actually 2 inches shorter than that of a regular" 500 scope. However  given the shape of it, i.e a basic extruded shape (no joggling at the end for example, or any machining), I could literally just cut to length !    Then just drill couple holes for the screws holding it to the chassis, and that's it. So I was starting to look closely at the holes on the chassis of the 575, and noticed something odd.... the hole are.... not.... countersunk ! But they HAVE to be in order for the screw to fit ! It's just not possible otherwise !!! So that had me baffled.. only explanation is that there NEVER was a beam in there, despite the logic, and despite the hole being present !  I t was hard to believe but the evidence was there, pretty compelling... so I rushed to Tekwiki to check pics of the 575.... and what do you know... pics do NOT show a beam on the left side either ! Checked again, this time for B&W pics in the service manual... still no beam !    Then checked the 531A... THE SAME !!!     

So all this time I thought I missing an obvious, huge piece of the chassis, and in fact there was nothing missing to begin with ! 

So that's one problem "fixed" kind of ! 



Then turned my attention to the 4 crapacitors soon to be replaced.

I pulled / desoldered a few wires so I can take them all out of circuit to make reliable/meaningful measurements. Before touching any wire, made sure to take a good close-up pic of all the wiring pertaining to these caps, so I can put it back properly... my memory is not that great and after only one hour I cna come back to the bench and already start wondering where the hell THIS wore goes to ! 
So since it will take a few days for the caps to arrive, no choice... PICTURE ! 

Then I could measure them all one by one.

1) Capacitance : they are rated at 2000uF  but no indication of tolerance on the cans or part list... but from memory on other scopes, it can be as wild as -50/+100% !!!     3 of them read 3000uF and one read 2680uF.

2) Shorted / discharged all the caps, the moved on to DC resistance check. This one was a bit weird. At first, it's a short for a split second then very quickly climbs up to 3K or so, the slows down dramatically and slowly keeps climbing. After a few seconds it gets to 20 or 30K, then stops there. Not good. Then if I remove the probes, and put them back on like almost immediately, a second or two, then it now reads much higher. Depending on caps, 750K or 1.5M or 3M tops. But it does not climb. It just reads this value instantly and sticks to it.

No sure I understand 100% what's going on. However what I do understand is that the max they will read is in the order of 1M give or take, which can't be good for a capacitor eh ?!.....
So they do need to go indeed !

Tried to remove on these caps just to see how easy it goes. It's a nightmare : The 4 ground tabs go through a narrow slit in the base that's screwed to the chassis, then the tabs are twisted to lock the cap onto the base. OK so I though I just need to remove the solder, straighten the 4 tabs and it should come out just fine.... nope, forget it. The tabs impossible to straighten well enough to even remotely hope for them to go back through the narrow slit they were inserted into when new. Plus, the tabs are perverse and feature a "locking" mechanism, so to speak. It's like two little "spikes" on either side of the tab, they "expand" when you twit the tab to lock it, and then act as an ratchet thing... you can twist one one, it's locked, then the spikes fighting and keep the tab from being twisted back in the other direction. Plus, doing this in situ just makes things more difficult.. and you have FOUR oof these monstrous tabs per can... and TEN cans in the instrument, should you wish to pull them all !  So instead I had to resort to removing the two screws that hold the base onto the deck, problem solved. However access to the head of tehse screws, top side of teh deck, is absolutely terrible. I managed to get one cap out as an exercise... but that's it. I will put it back where it can from, and won't touch the other cans, like ever.
So the new caps will have to be soldered bottom side, I am not going to go though the trouble of "restuffing" the cans. Will just pull one wire to disconnect them, then solder the new caps straight to the tabs.  Like MED did on his 547. It's ugly, looks out of place, looks not period, but... I will have to live with it...

Second thought.... OK maybe it's possible to remove these cans.. just had another look. It's kind of a domino game : now that I have removed one, it gives me access to the screw of the next can, then the next, and so on. As for the second row of cans, hidden in the center of the scope, the screw that's behind the cans is 100% inaccessible because there is a large aluminium panel  all over that area... it's the sub-chassis for the collector sweep stuff, on the other side of the chassis ! So.... if I remove this entire sub-chassis, then I can get access to the screws and remove the cans. But removing the chassis is not a 2 second job... it's tied to a big transformer, so some wires to pull, and also tied to the front of the chassis, the face plate, because it hold 3 rotary switches. Knobs are connected to the switched via shaft couplers, so you need to free those 3 couplers, in situ, with crap access.. one is close to you it's OK, but the last two are buried in the center of the scope.. normal Allen Wrench won't do ti, no access. Only way is to get a dedicated 1/16" screw driver, and a long one so you can reach the couplers without having to shove your hand inside the scope or else you don't see what you are doing and you don't have space to manoeuver / turn the screw driver....

So I ordered a crew driver... cheapest I could find was an extremely ugly looking "WERA" branded thing, looks like a Rigol style wise, but for screw drivers...

https://www.amazon.fr/Wera-Kraftform-Tournevis-argent-05118076001/dp/B001555FYK/ref=sr_1_5?__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&dchild=1&keywords=1%2F16+tournevis&qid=1631748425&sr=8-5

6 euros plus 5 for shipping, but at the checkout Amazon said I have nothing to pay at still had some Euros left from an old coupon/voucher my ex-company gave me. So free screwdriver for Vince. Ugly one, but free..... no here is hoping it's gonna do that job ! Have a 1/16" tiny Allen wrench and the size is ACTUALLY is, is 1,5mm instead of 1,6... so it can't grab the head, it spins round and round in it ! 
On the SAME set of wrenches, I have also METRIC wrenches. I tried the 1.5mm one, hence should have the exame same problem, too small... and I do, using ONE side of the wrench (the small side)... but somehow the OTHER side (long side) of that same wrench... fits PERFECTLY ! 

So... cheap wrenches can be pretty much useless, beware !

Anyway, I have order the caps. Didn't get them from Farnell to save money (minimum order 35 Euros for free shipping). So I searched a few smaller suppliers to see if they had decent caps, and then checked how much they charged for shipping... overall the best deal was not from a French shop, but from Reichelt in Germany. 13 Euros delivered for 10 caps, top quality, Nippon-Chemicon, 105°C rated for 10.000 hours.  No 2000uF 20V as originals were, so grabbed closest, 2200uF (+/- 20%) 25V.

Also ordered the cheap component tester, can't wait to play with this thing, like millions before me already have ! 

OK that's it for today... now waiting on the things I ordered...

[xrunner]

Good write-up. Interesting about that "missing" beam that isn't really missing. I guess that side is sufficiently solid what with that mid-tier circuit assembly. But why did they drill holes ... the answer my friends, is blowin in the wind. 

[tautech]

Caps done P-P wiring on a big tag strip will solve all them headaches. 

Good write-up. Interesting about that "missing" beam that isn't really missing. I guess that side is sufficiently solid what with that mid-tier circuit assembly. But why did they drill holes ... the answer my friends, is blowin in the wind. 

No doubt the drillings for a beam in the front panel are for other models that use the same panel.

[Vince]

Yes that's what I think too.

Most 500 scopes, I mean the "big"/mainframe ones, not the smaller monolithic ones, have the same cabinet dimensions, so same front and rear panel. They just need to punch different holes in the web to cater for the various models / knobs layout

So I looked at another 500 scopes on Tekwiki.. picked the the 547 because why not, to see it were fitted with two beams.

Turns out still NOT !    Still missing a beam but... NOT the same one ! 
575 has the LHS one and is missing the RHS one.. 547 it's the other way around !
And again has holes, not countersunk, on the missing beam side.

So yeah, all rear and front panels are manufactured the same and they just screw the beam on whatever side they fancy, depending on the particular model.

I still find it lame to skimp on a beam, as I find it serves also a mechanical role to support the side panel / cover ! It can rest on it. Without the beam it's much more easily bent should the scope get dropped or something heavy be dropped onto it 

[Vince]

Finally found the tolerance for the crapacitors.

The parts list I should have read more carefully... at the start of the capacitor section, it says : " +/- 20% unless otherwise stated ".

So these 2000uF caps should be no more than 2400uF, and are 3000uF, so definitely not very fresh... coupled with the weird and low resistance measurements, it's definitely time for them to retire....   

Oh, forgot also : before messing with the caps I measured ripple. 65mV or so on a non RMS DMM. So let's say 200mVpp. A bit much but I guess... hopefully that explains the ripple I saw on the traces on the CRT. We shall measure ripple again with the new caps installed...

[xrunner]

So these 2000uF caps should be no more than 2400uF, and are 3000uF, so definitely not very fresh... coupled with the weird and low resistance measurements, it's definitely time for them to retire....   

Yep. And leaving aside whether new caps are better made or not, they will still be smaller, so you'll have that "wimpy" small look we all deal with. 

[jdragoset]

As to the missing chassis beam dilemma, Consider the curve tracer has no front-to-back support on the CRT side but does have a hefty chassis on the opposite side about 2/3rd from bottom.
The 547 does have a support beam on the CRT side near the top

[Vince]

As to the missing chassis beam dilemma, Consider the curve tracer has no front-to-back support on the CRT side but does have a hefty chassis on the opposite side about 2/3rd from bottom.

You mean the vertically mounted heat sink for the two power germanium transistors ?!
This is no help whatsoever as it is only screwed along its bottom edge to the side of the upper deck, but that's it. So it provided zero support to anything, it's just holding itself...
Could be considered a stiffener if it were also bolted to the rear panel, but it's not.

However the 575 does have a big triangular stiffener on both sides, holding the rear panel to the bottom deck. So that does provide a good bit of reinforcement.

Just received my " WERA"  1/16" long (16cm total) hex screw driver, boy that was quick ?!    Ordered it from Amazon, maybe it came direct from their warehouse I guess, hence the swiftness.
Cost 10+ Euros shipped (about 50/50).

Just tried it for its intended purpose : help me reach and detach the 3 shaft couplers that hold the collector sweep sub-chassis to the front panel.
Driver fits absolutely perfectly. 4 set screws per coupler so 12 set screws total. Tried them all. Driver fits in each and every one of them like a glove. Gets in there in a split second, you don't have to "search" for minutes for the driver to "find" its way into the head. And once it's in, you get just a split hair of play, just way you want, no more. Tried it on a few knobs on the face place, perfect too.

Phew, I did not waste my money then, I got meself a great tool that will make working on this Tek or any other American boat anchor, a breeze ! 
Overall quality is very good too. Night and day compared to my set of cheap precision screw drivers.
This Wera has everything I would want it to have. Good finish, the top part turns freely, yet with minimal play. It's colour coded to tell you it's for a Hex head, and the size of it written clearly i large letters " 1/16" " as well so you don't have to guess.

So I bought this "Wera" brand totally at random as it was the  only one available and was affordable.. but turned out to be a good surprise. Will not hesitate  to buy more screwdrivers from them when I need to.

Only downside, is the sheer ugliness of its handle, Rigol style. But since it's an otherwise great tool at an affordable price, I will forgive it...
So if I could find similar value for money with a less ugly design, I am all for it ! 
 

[jdragoset]

Sorry,
I'm referring to the long chassis with the inverted vacuum tubes

[Vince]

Ah, that would be the upper deck. The 547 has one too ! 

All 500 scopes have one, they have to, no choice, as it supports the main time base and trigger circuitry !

[alan.bain]

Did you manage to find a source for replacement transistor sockets for the front panel? Mine are very unreliable but the tek manual only gives the electronic replacement parts....not mechanical ones and I cannot find similar ones among the usual culprits.

[Mine still has selenium rectifiers for the +/-15V supply and for +100V, Ge for the sweep and all I have replaced are the electrolytics which kept failing and some NE-23s which became unreliable and led to the feedback loop being all over the place, but apart from that it is original and works well]

The 2N277 Power Ge transistor does leak a lot - about 150 ohms C to E one way round, but I don't really know these Ge transistors well and that's similar to a 2N174 that I found lying about!

[Vince]

Did you manage to find a source for replacement transistor sockets for the front panel?

Nope, never even considered replacing them, they work fine. I simply cleaned them with a bit of contact cleaner spray, of course, like any old socket/connector, but that's about it...

Mine are very unreliable but the tek manual only gives the electronic replacement parts....not mechanical ones and I cannot find similar ones among the usual culprits.

That's strange... I do have the mechanical parts list in my manual. I downloaded it from Tek Wiki as always :

https://w140.com/tekwiki/wiki/575

Attached below an extract of the parts list showing all the sockets used in the instrument.
Manual does not have the exploded views so I don't know which socket goes where in the instrument, but I would guess it's the one called " 4 PIN TRANSISTOR" P/N 136-095.

[alan.bain]

Thanks!  I've just been using the original manual with the instrument, didn't think of looking online when I already had one which was fine apart from needing a new plastic comb :-)  The online one clearly is more detailed.

575s are great. I've owned this one for over 20 years. When I got it someone had helpfully wired it for 110V operation and connected to the UK 240V mains, the only damage was to the fan motor (!)  Looking at the chassis it has also been dropped at some point in its life.

It worked fine until recently when the traces started to show loops i.e. the rising going part of the collector curve did not overlap the falling one at the same voltage which is a sure sign that the smoothing caps are dead and then the step generator became troublesome.  New NE-23s (5AB-BTs rather) sorted that.

[Vince]

Wow, 20 years, that's what I call a love affair !
It's a warrior as well, having survived a miswiring of the transformer !!! 

Need to rewire mine for 248Volts or whatever the highest setting is, before things start to smoke in there...

Had a look at the manufacturer datasheet via Mouser for these 5AB-BT bulbs, looks like it's the new name for the NExx part numbers... though the data sheet does not give any clue as to what the last two letters (after the dash) mean, somehow !  So you don't even know what you buy... 
Some of them have slightly different voltage characteristics, but some variants have the exact same electrical specs...
Poor datasheet it is 

How did you know you had bad neon bulbs ? I mean there are none on the front panel being used as visual indicators, so I assume you mean the ones inside the instrument that either serve as voltage regulators or clamping devices ? What symptoms did you experience that led you to suspect one or more of them were bad ?  Just routine checking/preventative maintenance ? You looked at the schematics for test points and came across one that dropped a voltage way too low or too high compared to spec ? Given the datasheet for the 5AB, voltage spec is pretty lousy to begin with, so must not be critical I guess...

[factory]

Had a look at the manufacturer datasheet via Mouser for these 5AB-BT bulbs, looks like it's the new name for the NExx part numbers... though the data sheet does not give any clue as to what the last two letters (after the dash) mean, somehow !  So you don't even know what you buy... 
Some of them have slightly different voltage characteristics, but some variants have the exact same electrical specs...
Poor datasheet it is 

They aren't that new, the GE glow lamp manual (2nd edition) from 1966 has them, 5AB (NE-23) is standard version, 5AB-B is an aged & selected version of the 5AB, no idea about the 'T'.




David

[Vince]

Thanks ! Nothing beats period catalogues for old stuff !   Plus they look cool, I love these old documents, much nicer than today's Word documents 

Interesting... these are RADIO ACTIVE ?!    
"mildly" so, they say, still !!! 
I understand everything on this planet is radioactive to some degree, including our own bodies, but adding the stuff purposefully in something a mundane as a freaking light bulb, wow... I hope at least they got thee dosage right and it's indeed "mild" enough to be safe... but what was the definition orf "mild" compared to today's standards ?! Who knows...
Looks like back in the day radioactive stuff was very fashionable, like the BeO thermal couplers for trannies we talked about recently on TEA ! 

Anyway, it says that ALL 5AB models are aged, all of them. The A or B suffix are selected for voltage only.
Call me cynical, but somehow I doubt that the 5AB manufactured today, the ones I saw for sale at one buck a piece on Mouser... are aged for 124 hours like the old catalog says. These days aging anything costs an absolute fortune, I don't see how they would retail them at only one buck a pop if they aged them for 124 hours.. or at all, not even 5 minutes... 

Anyway, you wet my appetite with this nice datasheets, so I just searched for  and downloaded that GE catalogue. Glad I did ! 124 pages, 80% of it begin unexpected but very cool technical stuff about the million possible uses for neon lamp, never imagined you could do so much diverse stuff with these things, digital logic, frequency dividers ?! 
Complete with theory, diagrams, graphs... that's one hell of a gold mine !

[alan.bain]

I just was doing standard fault finding of the sweep amplifier and found that the "+1" amp output was -25V with an input of zero and it became clear the anode of the diff amp was at +250V or so and the grid of the kathode follower after it at -100ish which clearly suggested something was up with the neon between (it should basically drop 60V or so and obviously the feedback loop was pushing the diff amp to max output). Checking its wires had corroded close to the ampoule - replacement with one from a panel indicator confirmed the diagnosis.

I also found a problem with the pair round the intensity control.  Others were flickering rather badly so just decided to replace the lot.

It's fun to fault find and see that very precise staircase waveform on the scope from a very analogue looking device!

[Vince]

I just was doing standard fault finding of the sweep amplifier and found that the "+1" amp output was -25V with an input of zero and it became clear the anode of the diff amp was at +250V or so and the grid of the kathode follower after it at -100ish which clearly suggested something was up with the neon between (it should basically drop 60V or so and obviously the feedback loop was pushing the diff amp to max output). Checking its wires had corroded close to the ampoule - replacement with one from a panel indicator confirmed the diagnosis.

I also found a problem with the pair round the intensity control.  Others were flickering rather badly so just decided to replace the lot.

OK OK.... so they were bad indeed ! Since there are many of them in these old Tek scopes, and since I have so many of these scopes... I guess why not just buy 50 of them to have some stock at hand...

It's fun to fault find and see that very precise staircase waveform on the scope from a very analogue looking device!

Yeah I am hoping I can get mine to be clean and sharp ....getting there.  Will recap the entire thing and go from there.
As for the 2N277 Ge power tranny I already bought a NOS replacement one. No idea if it's good or not but at least I can compare it with the old one, I mean compare C-E leakage. According to the schematics though, looks like even if it were leaky, it would not cause much harm... it just supplies base current for the tranny under test. So as long as the base current looks OK on the screen, then well, the 2N277 is still good enough I guess...

[Neepa]

Interesting... these are RADIO ACTIVE ?!    
"mildly" so, they say, still !!! 
I understand everything on this planet is radioactive to some degree, including our own bodies, but adding the stuff purposefully in something a mundane as a freaking light bulb, wow... I hope at least they got thee dosage right and it's indeed "mild" enough to be safe... but what was the definition orf "mild" compared to today's standards ?! Who knows...
Looks like back in the day radioactive stuff was very fashionable

I don't know about the stated "dark effect" in the catalog page but back then radioactive elements were added to get the aluminium alloys of the day to the required tensile strengths in some applications.
Might be the same here where they needed to spice up the Tungsten filament to whatever spec they desired.

How I know that? Well, as a turbojet mechanic in training I'm being trained or have trained with an GE J79-17A (F4F Phantom II) and Orenda 14 (Canadair F86 subvariant) engine and those feature cast aluminium casings containing several percent of Thorium. They're harmless know though we have to be careful with these so we don't produce any chips or dust one could breathe in.

[DC1MC]

The only thing better than a 575 is a 576 and this is your last chance to buy an overpriced one 

https://www.ebay.de/itm/224697429564

Cheers,
DC1MC

[Vince]

I much prefer the 575 !  576 and 577 look ugly and are overpriced, are fragile with plastic bits that fall apart, and unobtainium parts inside that are prone to failure I remember, and routinely goes 2500/3000 Euros " as is, take it or leave it " ! 

I will keep my 575 thank you ! 
OK the 576/577 do have a large square CRT that's well suited to display networks of curves, I give them that but.. I don't care, my glowing 575 just has so much more character, I love it to bits ! 

For pure enjoyment and charm, I would go for a 575 any day of the week. However if one actually needs a curve tracer to do real work, run a business and make money from it, and doesn't give a shit about anything but pure technical specs and features, then yes I guess the more modern 576/577 are better of course.... if you have the skills and time to restore them to make them reliable and calibrated.

That ebay ad was already posted on TEA.... IIRC yesterday it was 400+ Euros, now 500+... and almost 2 days still to go ! No doubt it will reach 2000+ like the others before it... not for me thank you ! 

[factory]

Interesting... these are RADIO ACTIVE ?!    
"mildly" so, they say, still !!! 
I understand everything on this planet is radioactive to some degree, including our own bodies, but adding the stuff purposefully in something a mundane as a freaking light bulb, wow... I hope at least they got thee dosage right and it's indeed "mild" enough to be safe... but what was the definition orf "mild" compared to today's standards ?! Who knows...
Looks like back in the day radioactive stuff was very fashionable

I don't know about the stated "dark effect" in the catalog page but back then radioactive elements were added to get the aluminium alloys of the day to the required tensile strengths in some applications.
Might be the same here where they needed to spice up the Tungsten filament to whatever spec they desired.

How I know that? Well, as a turbojet mechanic in training I'm being trained or have trained with an GE J79-17A (F4F Phantom II) and Orenda 14 (Canadair F86 subvariant) engine and those feature cast aluminium casings containing several percent of Thorium. They're harmless know though we have to be careful with these so we don't produce any chips or dust one could breathe in.

The radioactive additives are for neon glow lamps used in this & other test gear, not filament lamps. Neither the GE book or Signalite book mention what the radioactive isotope used is.
But I have seen larger voltage reference glow tubes (eg. OA2) that are labelled as containing a tiny amount of Krypton.

David