Tektronix Type 575 curve tracer : repair and restoration

[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 !