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Restoring a TV-7/U Tube Tester



 
 
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  #11  
Old October 16th 14, 09:25 AM posted to rec.audio.tubes
Patrick Turner
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Posts: 3,964
Default Restoring a TV-7/U Tube Tester

On Tuesday, 14 January 2014 11:59:43 UTC+11, hugeshows wrote:
> Hello all,
> >

> Just picked up a TV-7/U tester today. I've used these before many times, and I've owned a few testers over the years, but never a TV-7 until today. I'm pretty happy with it, but it does have some issues.
> >

> I'm going to go over the whole process of restoring it so I might as well do it here.
>
> Here are a couple pics. One is the unit as it looks from the outside, and as you can see somebody decided to make a hole in the top and move the power cable. Also, there's a pic of the inside where a really sloppy set of diodes was put in.
>
> https://www.dropbox.com/s/z90wa6laqkpj46t/TV7_top.jpg
>
> https://www.dropbox.com/s/yac82k8agl...%20%281%29.jpg
>
> So, there will be some work to do here! Already, I have noticed that while the line check seems ok on this tester, every tube I've tested so far has been showing perhaps half of the reading it should be getting. The meter movement seems ok, but something is amiss...
>
> I've worked on several testers before, B&K, a Hickock here and there (TV7s are mostly Hickocks), and some oddball older ones of dubious quality. So I'm a bit green on this one, if anyone sees me screwin' up, please chime in.

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  #12  
Old October 16th 14, 01:21 PM posted to rec.audio.tubes
Peter Wieck
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Posts: 2,412
Default Restoring a TV-7/U Tube Tester

On Thursday, October 16, 2014 4:25:39 AM UTC-4, Patrick Turner wrote:

Much snippage

>
> I was given maybe 4 tube testers over the 20 years after 1993 when I decided to become as near an expert as I could with audio amps and radios using tubes.


> I never came across a tester from 1960s which may have actually survived the technicians who used it. In theory, if any tube has an internal short circuit then it should not hurt the tester if you plug it in with correct switch settings.
>


> I also have a few ancient tubed oscilloscopes, and some dismantled vacuum tube voltmeters. All are complete junk compared to much stuff I have acquired which was made after 1980, with not a vacuum tube to be seen.


I keep two testers - a diddly-simple Simpson emissions-tester that also handles shorts and gas that fits 99-44/100ths of the need, and a very nice, well-kept, properly calibrated Hickok 539B late of the GE Re-Entry Systems Division in Philadelphia before it closed down these many years ago. Both have been out-of-case cleaned and calibrated (in the case of the Simpson, to the extent it can be) and both do nicely.

At the same time, the only valid test of any vacuum tube is its circuit. A tester is not much more than a go/no-go device in most cases.

Getting to that 66/100ths use(s): Matching. Some few circuits prefer reasonably matched tubes at least initially. And very, very few testers are capable of actually matching. The Hickok 539 series (A,B,C) can match - albeit with one or two additional outboard VOMs attached.

And, of course, the big honking tester with three meters and enough switches to be massively confusing does impress the impressionable.

I do have all the update pages (through 1990 anyway) for both testers, so there are few tubes that are not listed. And I have acquired WE test data for the Hickok - as they made the WE testers under license.

But with all of that, and all the equipment that passes through my hands the either tester seldom sees the light more than 3 or 4 times per year outside Kutztown, where the 539 is in heavy demand by the tube vultures - the club performs free tests at the Clinic table.

Peter Wieck
Melrose Park, PA
  #13  
Old October 18th 14, 07:19 AM posted to rec.audio.tubes
Patrick Turner
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Posts: 3,964
Default Restoring a TV-7/U Tube Tester

Peter W wrote :-

I keep two testers - a diddly-simple Simpson emissions-tester that also handles shorts and gas that fits 99-44/100ths of the need, and a very nice, well-kept, properly calibrated Hickok 539B late of the GE Re-Entry Systems Division in Philadelphia before it closed down these many years ago. Both have been out-of-case cleaned and calibrated (in the case of the Simpson, to the extent it can be) and both do nicely.

At the same time, the only valid test of any vacuum tube is its circuit. A tester is not much more than a go/no-go device in most cases.

Getting to that 66/100ths use(s): Matching. Some few circuits prefer reasonably matched tubes at least initially. And very, very few testers are capable of actually matching. The Hickok 539 series (A,B,C) can match - albeit with one or two additional outboard VOMs attached.

And, of course, the big honking tester with three meters and enough switches to be massively confusing does impress the impressionable.

I do have all the update pages (through 1990 anyway) for both testers, so there are few tubes that are not listed. And I have acquired WE test data for the Hickok - as they made the WE testers under license.

But with all of that, and all the equipment that passes through my hands the either tester seldom sees the light more than 3 or 4 times per year outside Kutztown, where the 539 is in heavy demand by the tube vultures - the club performs free tests at the Clinic table.
Peter Wieck
Melrose Park, PA

Tube testers are fascinating creatures which attract many tube enthusiasts who lived through the USA's golden age of tubes.
I never acquired one worth maintaining after repairing / calibrating.

If I really want to understand a tube type when building yet another power amp, say using EH6550, then I can experiment with a test amp circuit with tube at wanted idle conditions anywhere for between heavy class A with low Ea and high Ia and class AB with high Ea and low Ia. But regardless of the class of the amp the majority of use with a 6550 will be class A with Ea high and Ia low, and also Eg2 at lower than Ea, and at moment I am finishing a pair of 300W amps with 12 x 6550 so I have B+ at +510V at idle, dropping to +450Vdc at 300W into 3r0 and Ia = 40mAdc, for idle Pda = 20W. There is cathode bias giving Ek = 23V, and fixed bias at -15.6V, and B+ for Eg2 begins at a regulated +358V but falls 20Vdc when sine wave testing at 300W. But without the B+ rails sagging, peak power is about 350W with 3r0 load.

From many observations or Vac and Iac I can deduce that at the idle condition of Ea = +473V, Eg2 = +338V, Ia = 40mA, Ig2 = 3.6mA, Eg1 = -38.1Vdc.
The gm for g1 = 5mA/V, and for g2 = 0.8mA/V. I also estimate tetrodee Ra = 35k.

None of these gm and Ra figures agree with tube data for tubes in data books because they measure gm with high Ia and low Ea, thus getting much more gm and lower Ra. None of this matters because all that does matter is that the EH6550 is fairly close to old samples of USA made 6550 and MOV KT88. Russian EH6550 and KT88 are virtually identical.
Knowing the gm of g1 AND g2 and knowing the Ra for the exact idle condition allows me to model the tube as current generator with current generated by TWO grids sitting in the electron steam, g1 having 5mA/V effect on Ia, and g2 having 0.8mA/V effect. The current gene model has infinite R between its 0V terminal and output, and to make it resemble the tube, 35k is strapped across the source as a shunt R which sets the Ra. My website shows TWO current gene models in parallel for tetrodes, one for g1 and one for g2, with one 35k R across both genies. So once you apply a load value for class A, all other voltages and currents can be worked out easily to let me know what I might expect before I hook up the tube. Or it tells me about what to expect with an old amp which is in triode or UL or pure tetrode.

Unless a tube tester could allow me to set up a 6550 with a wide range of Ea, Ia and Ia and Ig2, and then give automatic read-outs for Ra, G1 gm G2 gm, and do it quicker and more accurately than I do it "by hand", then it is of limited use. I do have TWO tests circuits for power tubes which I have used to confirm experiments BEFORE writing up yet another webpage about tubes in power amps, even those with power tubes in series.

If I had to service a color tele, or even a humble black and white one, or a complex tubed SW receiver, then if a stage isn't working, then the tube in the stage can be tested to see if its the tube or one of the surrounding R, C or L parts etc. Handy. But I have only ever serviced one Racal radio which had 3 mixers, and no TVs. AM and FM radios are easy by comparison, and audio amps are dead easier still, without a tester.
My toast to all testerators.
Patrick Turner.
  #14  
Old October 30th 14, 05:13 AM posted to rec.audio.tubes
hugeshows
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Posts: 29
Default Restoring a TV-7/U Tube Tester

On Saturday, October 18, 2014 2:19:02 AM UTC-4, Patrick Turner wrote:
> Peter W wrote :-
>
> I keep two testers - a diddly-simple Simpson emissions-tester that also handles shorts and gas that fits 99-44/100ths of the need, and a very nice, well-kept, properly calibrated Hickok 539B late of the GE Re-Entry Systems Division in Philadelphia before it closed down these many years ago. Both have been out-of-case cleaned and calibrated (in the case of the Simpson, to the extent it can be) and both do nicely.
>
> At the same time, the only valid test of any vacuum tube is its circuit. A tester is not much more than a go/no-go device in most cases.
>
> Getting to that 66/100ths use(s): Matching. Some few circuits prefer reasonably matched tubes at least initially. And very, very few testers are capable of actually matching. The Hickok 539 series (A,B,C) can match - albeit with one or two additional outboard VOMs attached.
>
> And, of course, the big honking tester with three meters and enough switches to be massively confusing does impress the impressionable.
>
> I do have all the update pages (through 1990 anyway) for both testers, so there are few tubes that are not listed. And I have acquired WE test data for the Hickok - as they made the WE testers under license.
>
> But with all of that, and all the equipment that passes through my hands the either tester seldom sees the light more than 3 or 4 times per year outside Kutztown, where the 539 is in heavy demand by the tube vultures - the club performs free tests at the Clinic table.
> Peter Wieck
> Melrose Park, PA
>
> Tube testers are fascinating creatures which attract many tube enthusiasts who lived through the USA's golden age of tubes.
> I never acquired one worth maintaining after repairing / calibrating.
>
> If I really want to understand a tube type when building yet another power amp, say using EH6550, then I can experiment with a test amp circuit with tube at wanted idle conditions anywhere for between heavy class A with low Ea and high Ia and class AB with high Ea and low Ia. But regardless of the class of the amp the majority of use with a 6550 will be class A with Ea high and Ia low, and also Eg2 at lower than Ea, and at moment I am finishing a pair of 300W amps with 12 x 6550 so I have B+ at +510V at idle, dropping to +450Vdc at 300W into 3r0 and Ia = 40mAdc, for idle Pda = 20W. There is cathode bias giving Ek = 23V, and fixed bias at -15.6V, and B+ for Eg2 begins at a regulated +358V but falls 20Vdc when sine wave testing at 300W. But without the B+ rails sagging, peak power is about 350W with 3r0 load..
>
> From many observations or Vac and Iac I can deduce that at the idle condition of Ea = +473V, Eg2 = +338V, Ia = 40mA, Ig2 = 3.6mA, Eg1 = -38.1Vdc.
> The gm for g1 = 5mA/V, and for g2 = 0.8mA/V. I also estimate tetrodee Ra = 35k.
>
> None of these gm and Ra figures agree with tube data for tubes in data books because they measure gm with high Ia and low Ea, thus getting much more gm and lower Ra. None of this matters because all that does matter is that the EH6550 is fairly close to old samples of USA made 6550 and MOV KT88. Russian EH6550 and KT88 are virtually identical.
> Knowing the gm of g1 AND g2 and knowing the Ra for the exact idle condition allows me to model the tube as current generator with current generated by TWO grids sitting in the electron steam, g1 having 5mA/V effect on Ia, and g2 having 0.8mA/V effect. The current gene model has infinite R between its 0V terminal and output, and to make it resemble the tube, 35k is strapped across the source as a shunt R which sets the Ra. My website shows TWO current gene models in parallel for tetrodes, one for g1 and one for g2, with one 35k R across both genies. So once you apply a load value for class A, all other voltages and currents can be worked out easily to let me know what I might expect before I hook up the tube. Or it tells me about what to expect with an old amp which is in triode or UL or pure tetrode.
>
> Unless a tube tester could allow me to set up a 6550 with a wide range of Ea, Ia and Ia and Ig2, and then give automatic read-outs for Ra, G1 gm G2 gm, and do it quicker and more accurately than I do it "by hand", then it is of limited use. I do have TWO tests circuits for power tubes which I have used to confirm experiments BEFORE writing up yet another webpage about tubes in power amps, even those with power tubes in series.
>
> If I had to service a color tele, or even a humble black and white one, or a complex tubed SW receiver, then if a stage isn't working, then the tube in the stage can be tested to see if its the tube or one of the surrounding R, C or L parts etc. Handy. But I have only ever serviced one Racal radio which had 3 mixers, and no TVs. AM and FM radios are easy by comparison, and audio amps are dead easier still, without a tester.
> My toast to all testerators.
> Patrick Turner.


Thank you both for some valuable observations. One reason I find testers to be important is that they can both validate other observations found in-circuit, but moreover, if a tube has problems like a short, I'd much rather my TV-7 take the abuse than my amp. I'd much rather test a bunch of random used tubes in my tester than in anything I cared about.

Tube testers can also tell you other things, if you're keen to observe their behavior over a great number of individual tests. Often I find that the amount of time it takes for the needle to rise to given value tells you more about the tube than the value it actually manages to attain after several minutes of warm-up. Slow to rise tubes often under-perform in circuits in my experience. Also, you get to see things like odd wobbles and instability in the readings, which can indicate mechanical problems in the tubes.

All in all, I find testers to be quite valuable. Sure, they don't match for current draw or anything really in terms of real-world operation parameters, but they provide a way to validate other findings, as well as save any circuit you care about from some shorting, gassy nightmare that could otherwise befall it.

Cheers!
  #15  
Old October 24th 17, 06:29 AM posted to rec.audio.tubes
[email protected]
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Posts: 1
Default Restoring a TV-7/U Tube Tester

The type 83 can operate horizontally just fine, but in one plane, which the TV7 socket position does for you. Think filament sag as they heat up. In one direction, they will have more space so as not to touch the anodes.

Also, the link given for an 83 solid-state replacement will not work properly. You need to re-create the 15v drop the 83 has. Search for 83 replacements using zener diodes. These will work much more like an 83.
  #16  
Old October 24th 17, 01:16 PM posted to rec.audio.tubes
Peter Wieck
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Posts: 2,412
Default Restoring a TV-7/U Tube Tester

On Tuesday, October 24, 2017 at 1:29:53 AM UTC-4, wrote:
> The type 83 can operate horizontally just fine, but in one plane, which the TV7 socket position does for you. Think filament sag as they heat up. In one direction, they will have more space so as not to touch the anodes.
>
> Also, the link given for an 83 solid-state replacement will not work properly. You need to re-create the 15v drop the 83 has. Search for 83 replacements using zener diodes. These will work much more like an 83.


Three years late - but here you are. Welcome!

The link works fine from here.

You *do not* need to recreate anything special - the circuit as-given works just fine. As to Zeners, along the lines of William of Occam, eschew needless complexity.

When I replaced the 83 in my 539B, I used my calibration tubes (6L6 & 12AX7 & 80), I had taken readings with a good 83. With the drop-in replacement, the readings were within a couple of needle-widths. This did prove the concept.

Hickok put the two rectifier tubes on their sides for the space. That it works does not make it a good idea. The solid-state drop in neatly solves the problem and removes any doubt as to the efficacy of the 83. You pays you money, you takes you chances. These are not precision instruments at any level at all. They are useful to compare one tube to another, cull for obvious defects and failures and reasonably close matching if necessary. But, as always, the best test of any tube is the equipment it serves.

Peter Wieck
Melrose Park, PA
 




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