Test Equipment Anonymous (TEA) group therapy thread

[med6753]

I'm ready. Wires pre cut to length and stripped. Just waiting for the female connector that's supposed to show up tomorrow. Problem is last update on 12/07 had it still in Dallas, Texas. We'll see.

So what is it? Will be custom 500 series plug-in extender. But it will have certain accepted limitations. It's use will be limited to strictly troubleshooting plug-in's that don't pass a signal. Dead ones like the Type 1A4. It cannot be used for scope to plug-in calibration nor compensation. The reason is obvious. Unshielded and improperly terminated signal transmission. But that's OK because those functions CAN be performed with the plug-in installed. So once a plug-in is fixed take it off the extender and complete the calibration/compensation process.


 

[mansaxel]

What both phools tend to forget are the coils - these parts, which most electricians don't like because they are complex and non-linear. And these shitty bad parts are combined with a limited stiff mechanic system, a limited flexible mechanical system and a non-zero mass and are put into a non-linear static magnet field to form a so called loudspeaker. Yes, you can compensate for frequency gain and phase, but the convolution of complex signals can not be undone.

Put your money on the loudspeaker and the room. The rest is irrelevant. Basically.

[mnementh]

What both phools tend to forget are the coils - these parts, which most electricians don't like because they are complex and non-linear. And these shitty bad parts are combined with a limited stiff mechanic system, a limited flexible mechanical system and a non-zero mass and are put into a non-linear static magnet field to form a so called loudspeaker. Yes, you can compensate for frequency gain and phase, but the convolution of complex signals can not be undone.

Put your money on the loudspeaker and the room. The rest is irrelevant. Basically.

Speaking of which...

Anybody know anything about these Pinnacle Mini-Monitor speakers..?

Picked 'em up for $10 cuz I needed something of this form factor and they sounded passable good hooked up to a cheap AiO stereo at the Thrift; just curious if they're like one of those lost golden oldies of the MEBB age or "White Van Special" crappity-crap.

I can shoot a few more pix once I get in 'em; need to fix some drop damage and resultant bass-port broke loose.

mnem
 

[Specmaster]

Yes, but what do you measure for...? If you don't believe the difference exists, you aren't going to know how to set up your testing scenario.

How do you measure for the "warmth" of the sound, when that really is just a subjective description for how a particular tube distorts the signal going through it, which some people (usually musicians) prefer?

How do you measure for what is just the right amount of "fuzz" distortion or gated reverb, when that is entirely subjective, and dependent upon the artist's ear, which probably has suffered massive damage due to close proximity to the stacks for a decade or three?

I'm sure that folks who work in the trade... for example, those who worked with Phil Collins... can explain things like gated reverb and how to "get his sound", and could even identify it by sight from the trace on the screen of their favorite post-processing studio... but that is not the same as being able to objectively test for it.

Art is art and science is science... everything we as human beings do that is of import combines the two, and both are essential. FULL STOP.

mnem
 

If the sound of a valve amp is supposed to be "warmer" then clearly this must also show in the sound waves when fed into a scope, ie., feed frequencies into a solid state amp and record the resultant output waves and amplitude etc and then feed the identical frequencies into a valve amp and see what the output results are and on both amps bypass the tone controls. On decent systems, I would fully expect that no visible differences would be found. Yes there would be differences between cheap and cheerful systems as the design of amp would vary greatly. These audio phools are supposed to have systems that failthfully reproduce the signals fed into the inputs, so that the signals exiting from the outputs faithfully reproduce the input ones but at a far greater power rating, would sound exactly the same be it valve or transistor, anything else is not true Hi-Fi as either something is being lost or added to the sound.

[m k]

but I couldn't tell the which was the blue or black line

I'm quite sure there's very little if any blue left.

My educated guess used 3rd column as a reference and base argument was that pigments are turning lighter and not darker.

So 3rd column has something gray and something brown.
Black was probably made from single type of pigments, so gray fits.
Brown is then something else and all base colors mixed.
Also, if red is not red then there should be more red.

Nowadays it's usually magenta that dissapears first.

[McBryce]

You don't get it: if things are real, then there is ALWAYS science involved. How can this be narrow-minded?

You're completely ignoring the second half of my statement:

"Art is art and science is science... everything we as human beings do that is of import combines the two, and both are essential. FULL STOP."

I never said there wasn't science involved; only that art is also involved and is just as important as the science.

Take the very engineering we discuss in here; it is very science-heavy; however, part of being a good EE is picking the right way to make a circuit to do something, or how you go about deciding which is the better way to do it.

This is as much to do with the art involved in engineering; that judgement developed over years and decades of doing it right or doing it wrong, the lessons learned therein, and sometimes just a best educated guess at how to get there within the time and cost restraints imposed.

Otherwise, you could just tell a computer what you want a circuit to do and let it design the damned thing.

mnem
 

My english isn't good enough to take this discussion further. But here are a few points:
- Art can ONLY happen under the laws of science. Art CAN'T exceed the laws of science (here: physics)
- "right way", "better way" is simply bla-bla with no meaning. This is okay to impress stupid people but not engineers.
- "Otherwise, you could just tell a computer what you want a circuit to do and let it design the damned thing."
   ---> Argument non sequitur https://en.wikipedia.org/wiki/Formal_fallacy

I have to disagree with you on the second point: ""right way", "better way" is simply bla-bla with no meaning. This is okay to impress stupid people but not engineers."
Of course there are right ways and better ways to do things. Go back to ANY circuit you designed in the past and tell me that you would do it exactly the same way again this time. There are always things that could be improved. If you think that science / engineering gets it right first time, then you haven't worked in the real world.

McBryce.

[factory]

Something in the round-tuit pile that needs revisiting, the Yokogawa/HP 4350A high capacitance meter.



This had multiple problems, most I suspect caused by a previous owner/users & a charged cap accident and the other a destroyed bias switch.
Damaged parts found included one of the op-amps, a transistor and burnt resistor, needs further investigation.





Also a note that certain hp coded transistors that have different pinouts, for the same part number due to being sourced from different suppliers. 


It will be interesting to see if anyone has the 4350B (no leakage current measurement).
https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1972-03.pdf

David

[BU508A]

I have to disagree with you on the second point: ""right way", "better way" is simply bla-bla with no meaning. This is okay to impress stupid people but not engineers."
Of course there are right ways and better ways to do things. Go back to ANY circuit you designed in the past and tell me that you would do it exactly the same way again this time. There are always things that could be improved. If you think that science / engineering gets it right first time, then you haven't worked in the real world.

McBryce.

I do agree with you, but only, if the following pre-condition have been met:
Defining in a quantative way, what "better" means.

Example:
1) Better in terms of "lower S/N ratio" or "lower THD": yes.
2) Better in terms of "warmth sound" etc.: no.

And mnem's assertions go in the direction of point two. Imo.

[Neomys Sapiens]

... As for dying not even sure I would have to go there, ..

While we all will have to accept that reality at one time, I would advise you not to accelerate it.
As far as dyeing is concerned, I'll leave it to your taste.
 

[Vince]

Bah..... I keep doing that typo, I just can never get it right somehow 

[Cerebus]

Also does one perforate the leather piece before hand, to make way for the sewing needle, or does the needle do its own hole as you along...
If need to perforate before hand, I guess you need some kind of appropriate tool to make it look good and have holes with an even consistent diameter, looks and spacing/pitch... 

Yep, with a Pricking wheel....look it up. 

Only for girly weight leather. For heavier leather (e,g, bridle leather) you use a pricking iron which needs whacking with a mallet.



My No. 7 pricking iron and a bridle leather mobile phone case I made about 15 years ago that it was used on .

[Vince]

Also a note that certain hp coded transistors that have different pinouts, for the same part number due to being sourced from different suppliers. 

Wow I never heard about that one, how practical !! 

[Vince]

Also does one perforate the leather piece before hand, to make way for the sewing needle, or does the needle do its own hole as you along...
If need to perforate before hand, I guess you need some kind of appropriate tool to make it look good and have holes with an even consistent diameter, looks and spacing/pitch... 

Yep, with a Pricking wheel....look it up. 

Only for girly weight leather. For heavier leather (e,g, bridle leather) you use a pricking iron which needs whacking with a mallet.



My No. 7 pricking iron and a bridle leather mobile phone case I made about 15 years ago that it was used on .

What do you know, there are leather people on TEA ! How lucky I am...
TEA is a one stop shop ! 

Glad to have you onboard, you're the man for my handle job ! 
Iron looks cool, sounds like a good solution, I like it.

OK great, I feel like my home made leather handle idea is not total day dreaming then, I am starting to get all excited about it now, my Tek scopes will look better than any other on the planet ! 

[Cerebus]

I don't care about "warmth" or other adjectives being used by audiophools, because there is NO definition, what "warmth" means in terms of quantity.

Oh that's easy. For most music it equates to a few dB boost across an octave or so just below middle C (i.e. 120-240 Hz or thereabouts) ideally combined with a little frequency conscious peak limiting above around 4kHz.

[WastelandTek]

It is certainly true that we lack the language to meaningfully discuss the nuances here.  People start sounding like wine snobs..."vaguely floral with a hint of nutmeg, a sharp but dark finish."

[srb1954]

Something in the round-tuit pile that needs revisiting, the Yokogawa/HP 4350A high capacitance meter.

Is just a coincidence that this post appeared of page 4350 of this thread or was this deliberate timing?

This had multiple problems, most I suspect caused by a previous owner/users & a charged cap accident and the other a destroyed bias switch.
Damaged parts found included one of the op-amps, a transistor and burnt resistor, needs further investigation.

This is a nice little meter. I haven't had much trouble with mine after the usual replacement of tired electrolytics. I have found it fairly robust and haven't managed to damage it with charged caps.

One modification I have made is to reduce the size of the filter cap (A4C6) on the bias supply adjustment pot from 220u to 100u. With the original value cap the bias voltage indication on the meter considerably lags the actual bias voltage making it difficult to adjust the bias voltage without overshooting. Reducing the cap reduces the meter response lag making it much easier to adjust the voltage.

My next modification might be to replace the bias pot with a multi-turn device making it even easier to accurately adjust the bias voltage.

[mansaxel]

These audio phools are supposed to have systems that failthfully reproduce the signals fed into the inputs, so that the signals exiting from the outputs faithfully reproduce the input ones but at a far greater power rating, would sound exactly the same be it valve or transistor, anything else is not true Hi-Fi as either something is being lost or added to the sound.

Thing is, they usually don't want that. If you give them something like a good studio monitor speaker, they'll dismiss it as clinical.

Take the Yamaha NS-1000. (NOT the NS-10, which is a piece of shit speaker (fact, even acknowledged by its admirers)) It is a remarkable revealing instrument. Very, very precise and correct. It was universally preferred by the engineers at the Radio here, in blind (don't remember if it was double) testing. They listened to recordings they'd made themselves,  of people they knew, speaking.  Quite demanding, I'd say.

Yet, it is universally disliked by the 'phool community here, especially the Carlsson gang. Stig Carlsson was a well-known speaker builder who had strange ideas on "filling the room with sound" and made quite uninteresting speakers with treble drivers pointing in all manners of directions. A comb filter hell. But he's got a devoted following. And in the tests, his speaker had already lost, to a Bang & Olufsen box.  Then the Yamahas came along and completely obliterated the competition.  And some in the Carlsson gang implies that Yamaha bribed their way in.  But I had colleagues that had been in the process, back in the 70s, who assured me that there had been a fair path to victory for the Yamahas.

Anyway, most 'phools wouldn't know what "correct" is even if it hit them on the nose.   

[xrunner]

Anyway, most 'phools wouldn't know what "correct" is even if it hit them on the nose.   

I wonder if they could even tell (or approve of) the sound of the real person or band if it was sitting right in front of them. My ideal blind listening experiment would be to put the phool in a chair and tell them they were going to listen to several systems or speakers moved in front of them, but they would not be able to see what it was. Unknown to them, one of the "speakers" or "systems" would be the actual live band or singer right behind a movable wall. The wall would be moved and the band would just play the song using their actual kit. Would the phool pick the live band as the best sound? I wouldn't bet on it.

 

[tggzzz]

These audio phools are supposed to have systems that failthfully reproduce the signals fed into the inputs, so that the signals exiting from the outputs faithfully reproduce the input ones but at a far greater power rating, would sound exactly the same be it valve or transistor, anything else is not true Hi-Fi as either something is being lost or added to the sound.

The audiofools cannot address one simple but important question.

Given an orchestra in an auditorium, where should they sit (or the microphones be placed) to hear the correct sound? In the wind section? By the conductor? In the first row, last row or somewhere else?

[Specmaster]

Also does one perforate the leather piece before hand, to make way for the sewing needle, or does the needle do its own hole as you along...
If need to perforate before hand, I guess you need some kind of appropriate tool to make it look good and have holes with an even consistent diameter, looks and spacing/pitch... 

Yep, with a Pricking wheel....look it up. 

Only for girly weight leather. For heavier leather (e,g, bridle leather) you use a pricking iron which needs whacking with a mallet.



My No. 7 pricking iron and a bridle leather mobile phone case I made about 15 years ago that it was used on .

What do you know, there are leather people on TEA ! How lucky I am...
TEA is a one stop shop ! 

Glad to have you onboard, you're the man for my handle job ! 
Iron looks cool, sounds like a good solution, I like it.

OK great, I feel like my home made leather handle idea is not total day dreaming then, I am starting to get all excited about it now, my Tek scopes will look better than any other on the planet ! 

Yep, it takes all kinds to make a talented group like this, and that's why the topics can go astray from time to time, but as has been also been said, we also very good at self policing, and all of that to mind at least makes this forum so very interesting and compelling reading, I look forward to logging on each day, and I always manage to learn something as well. 

[Specmaster]

These audio phools are supposed to have systems that failthfully reproduce the signals fed into the inputs, so that the signals exiting from the outputs faithfully reproduce the input ones but at a far greater power rating, would sound exactly the same be it valve or transistor, anything else is not true Hi-Fi as either something is being lost or added to the sound.

The audiofools cannot address one simple but important question.

Given an orchestra in an auditorium, where should they sit (or the microphones be placed) to hear the correct sound? In the wind section? By the conductor? In the first row, last row or somewhere else?

1000 times this, your hearing and perception of a performance, live or recorded is going to be coloured by your listening position

[Vince]

502A

Started probing around the thing. Printed the jigsaw schematics, taped them back in one piece so I can actually read them... then did the same digitally so I can show it to you. Just because I am nice of course. Been reading a bit the theory of operation chapters in the service manual as well.

3AM so am tired, will try to make it short(er than usual).

First tested the trigger section. AUTO MODE somehow doesn't work, but I don't care for now because NORMAL mode works : I fed the calibrator signal to the lower beam, the one I suspect kinda works. Trigger circuitry can pick up on it no problem, it produces lovely text book pulses in return, I am very happy.

So these lovely trigger pulses then go to the " Time Base Generator " as Tek calls it. Schematic below. Checked the output for a sawtooth, no luck , zero signal, just DC. Then checked the input of the circuitry at the other end... trigger pulses go through an RC differentiator to turn the square pulses into pin sharp pulses/spikes. That part works fine. Then these sharp pulses are applied to the grid of the first tube in there, V135A, the input of  multivibrator.
checked the output of this thing, ie plate of V145A / R148 as highlighted on the schematic. I get no signal, just DC.
Now, this multivibrator can be turned of if you flick the big XY switch on the side of the cabinet, to " XY" mode instead of "swept" mode. In swept mode, what I want to see working, the "tail" of the multivibrator, the two cathodes, are connected via this XY switch, to the -150V rail. So I operated that switch to make sure I got a solid -150V, and I do. So no problem there.

So that's good news I guess, I narrowed it down. I have trigger, a good signal going to the sweep circuitry.. but no sweep.

I also noticed that the RECURRENT mode does not work either. This mode is new  to me, never seen it in any other Tek scope, must be a 502A special...
From what I understand from the schematic and the Theory of operation, it's supposed, in the absence of a trigger signal, to make the multivibrator free run, just like it does in the Trigger section when you select AUTO.
When I switch to RECURRENT mode,, as you can see on the schematic I am supposed to get a triangular periodic signal at the input of the multivibrator... but all I get is DC.

So either another problem, or just another hint to steer me in the direction of a common problem.

Happy for now, more tomorrow....

MISC, I noticed that one of the 3 HV tube rectifiers in the CRT section, has been replaced, no doubt about that... looks newer / cleaner than the other two, and the soldering job on the ceramic strips is hardly factory grade...


Good night.

[med6753]

Recurrent Mode is what all old scopes had for sweep before Tek developed this thing called "Triggered Sweep". In recurrent mode you should always have a free running sweep and therefore a trace on the CRT. If you don't then that's exactly where you need to concentrate your troubleshooting. As I stated prior....sweep first. Worry about any trigger issues later.

[vk6zgo]

 Not that it does me any good for repairing test equipment, but there's a reason all those are pennies on the dollar and 6DJ8s are expensive. BECAUSE THE AUDIOPHOOLS THINK 6DJ8s ARE SPECIAL.

Guess what the 12.6V filament voltage version of the 6DJ8 is?

8416. Fuck me. 

And, in a properly designed audio circuit it can probably quite readily be replaced by a 12AU7, 12AX7, 12AT7, or whatever!

[vk6zgo]

Looking at both mine & your other 502A with the "ugly brown dielectric" UHF connectors, they are both US made.
The one you just acquired is Dutch made, possibly they sourced those UHF connectors locally and they happened to have the white dielectric.

Oops no, don't know where you got the S/N for my first 502A, but it was made in Holland just like the one I just bought... same factory/plant, first digit is ' 7 ' in both cases.

See the thread I started just 3 years ago when I got it. You can see the S/N on the close up pics :

https://www.eevblog.com/forum/repair/(classic)-tektronix-502a-scope-repair-restoration/

Old one is S/N 700068 and the new one is 701033 , so a thousand units newer, but still made in the same European plant.
Maybe at some point the plant momentarily ran out of the crusty brown ones for whatever reason, and all they could get hold off as a replacement in a hurry, were the white ones ? Was a temporary backup plan ? And 2 weeks later when they finally got the brown ones back in stock, they resumed using them ? Who knows, who knows.... 

Maybe the grey beards on Tekscope know the answer to that one...haven't posted on that forum in years...

Yeah it looked terrible from the outside, didn't help that it also had got rained on in the morning at the show, I couldn't go till the afternoon if I remember correctly. I guess the seller was happy to not have to take it back with him, not so much fun was carrying it all the way to the car park field.

It was quite grubby on the inside too, the trigger circuitry is much cleaner, due to the being directly under the top covers.

Wow that's gross ! 

This scope was really far gone, it was very lucky to meet you and get a new chance in life, and get a peaceful retirement ! 

I think "crusty brown" was pretty common, back in the day, although they were not originally crusty, new ones were transparent.

I always thought they were hard polystyrene, which has good RF characteristics, but maybe I'm wrong, as I can't remember the insulation being prone to melting when soldered, like the similar looking insulation of "Belling Lee" connectors.

The Marconi TV transmitters I have referred to several times, used them for their video input connectors (pre the general use of BNC for video).
They hadn't, from memory, gone crusty, although they were discoloured !

I think Polyethylene took over the market from the "crusty" stuff, & the earlier mica reinforced bakelite  (PTFE was a bit expensive for coax connectors, back in the '50s,although it was used elsewhere.)