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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 10th Feb 2019, 7:02 pm   #21
Radio Wrangler
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Default Re: Valve Testers

What I would like to do is catch those people who burn out dear old VCMs before they do so, and show them how to use them properly. I'm not a believer in AVO-tested valves acquiring magic fairy dust in the process, or that testing guitar amp valves will guarantee success like Clapton's bank account, but there are real reasons for wanting to match pairs (or check the balance of double triodes) and real reasons for checking valves.

The trouble is that to someone beginning, valve testers look like chunky, professional equipment and their fragility is invisible.

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Old 11th Feb 2019, 6:04 pm   #22
avocollector
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Default Re: Valve Testers

I always love the glorious advertising stories about the long plate vintage 1960's Rareashensteeth brand 12AX7's tested in the Avo mk V valve tester and how this will give you 'tone beyond belief' - for a modest $350 per unit. I plonk such things in with the 'tone sucking capacitors' in les Paul guitars, the gold plated connectors on guitar cords to 'noticibly reduce loss of highs' and last, but not least, the magic liquid you painted on the IC's in your solid state guitar amplifier to make it sound like a valve one nonsense. My amp gets whatever make I can find of the correct valve shoved in as a replacement and I've even left the 'tone sucking' capacitors in my Les Paul guitar. Perhaps the audio/guitar people will come to their senses or find some other quest to throw money at.

The sad thing is for those like myself who started to collect tube testers just for fun when prices were low but had to suspend it due to these activities - recall one of my early ones cost $25 - bog simple US type and still going today! I also have a non working one (forget the brand but definitely NOT an Avo) whose mains transformer and internals were so complex I hastily put it back together again for the wonderful day I get a round tuit. Have an old Palec one that uses an 01A valve, Taylor 45C and so on - was great fun until the audio/guitar valve people got in on the act. Now with the testers going for $125 and up for even a simple one, I've bowed out for now, But one day I WILL return - LOL.
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Old 11th Feb 2019, 6:10 pm   #23
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Default Re: Valve Testers

As a side issue the NZVRS bulletin had a replacement idea for the rare meter that goes bung in an Avo valve Tester (CT160) as it's some odd current like 33 micro amps FSD - basically, if memory serves me correctly, it used an op amp feeding into a more normal range meter. The point being there are work arounds even for the burnt out meter Avo testers - not that anyone selling one will ever admit the tester is in anything but excellent working condition.
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Old 11th Feb 2019, 6:20 pm   #24
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Default Re: Valve Testers

I think there are a number of 'papers' around describing such fixes and I do have one on mine, which needed an op-amp to correct one of the two 50uA meters. That, presumably, was suffering from some shorted turns. When selling, they'd be hard to hide as you need to put in a transformer to supply the op-amp with power.

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Old 12th Feb 2019, 6:32 pm   #25
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Default Re: Valve Testers

No one “owns” a thread, not even the OP. And I’m very pleased that members have an opportunity to exchange ideas about radio related items, even if they may not address the original reason the thread came into being. Having said that, I would be extremely grateful if anyone out there in Radioland had any information about how, in the absence of valve manufacturers’ data concerning them, emission test measurements should be interpreted.
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Old 13th Feb 2019, 8:00 am   #26
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Default Re: Valve Testers

Can't help you there, as I said before when I test valves I look at a mutual characteristics graph, like this one for the 6SN7 - see attached and find a place where Va, Ia and Vg cross. Here on this sheet it might be Va 225v, Ia 5mA, Vg -8v. So I'd start by setting Vg to -8v, turn on heater PSU, check it's at 6.3v , then bring up Va till it's at 225v, if the Ia meter reads 5mA or near, the valves a good un.

How a valve behaves when testing can tell you a lot, for instance, heater flash, if Va dances about or won't settle, or if Vg moves whilst bringing up Va might indicate a short or similar. After testing a few hundred valves you get to know when a valve is good or suspect. A good valve will slowly climb to the expected Ia, bad ones linger about about looking solemn and shifty whilst muttering under their breath : )

This chap did a few video's on valve testers you might find interesting - https://www.youtube.com/watch?v=TtVbTSAKx7k

Andy.
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Old 13th Feb 2019, 10:04 pm   #27
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Default Re: Valve Testers

Thanks very much Diabolical Artificer for the advice and the link which are most useful. I have never seen so many valve testers gathered together in one place and it is rewarding to realise the sheer diversity of human interest! I intend to broaden my search for the sought after information and, if successful, will post details here. Thank you all so much for your generous help.
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Old 15th Feb 2019, 5:45 pm   #28
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Default Re: Valve Testers

Also thanks very much Diabolical Artificer from me as well for the link to the video about the testers - great to see so many collected.
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Old 15th Feb 2019, 7:05 pm   #29
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Default Re: Valve Testers

Surely emission measurements can be easily checked, even for valves without an manufacturers' data?

Assuming a US, European valve then the cathode emission is simply limited by the area of the cathode and its temperature.

Can measure the area of the cathode by measuring, might have to bust open a valve to do so of course.

Can measure temperature using one of these heat cameras, or the colour.

There are lots of TV and radio valves that no one has any interest in so it is easy. and cheap, to get a baseline of area and temperature. Plot a graph and there you are.

If you want to do destructive tests then try a signal valve with 500V at 500mA on it, slowly. The point at which it glows red and then explodes will, again, be consistent and can show it with a few graphs.

Doing the same tests on modern valves could be instructive as well.
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Old 15th Feb 2019, 7:21 pm   #30
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Default Re: Valve Testers

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Surely emission measurements can be easily checked, even for valves without an manufacturers' data?

Assuming a US, European valve then the cathode emission is simply limited by the area of the cathode and its temperature.
Well, certainly with indirectly heated valves, which have a cathode, some valves will glow nicely and look fine, but have quite poor emission. Temperature alone is not the key issue; the physics and chemistry of the cathode material is critical and complex. There are volumes of technical papers written about cathode behaviour.

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Old 16th Feb 2019, 5:00 pm   #31
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Default Re: Valve Testers

Yes, indirectly heated.

As you say, there is lots written about cathodes but from my reading by the 1940's it was all pretty much known and standard. Whether this is still so for the new valves I don't know. So temperature, on European or US valves is still the defining emission limit.

If the temperature is known and emission is low then what more do you need to check?

Without going back to the books, the cathode material will energetically emit electrons at a temperature. It will do this until the whatever material in the cathode is depleted, poisoned or whatever. At this point the maximum emitting current drops from the data sheet value, or whatever is calculated to be a sensible limit, the valve is worn out.
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Old 18th Feb 2019, 12:53 pm   #32
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I have to admit to not being at all familiar with the Hickok testers, but obviously, they have come up with what looks like an attractive technique. Among the Avo testers, the VCM163 also uses a system which does not need a standard valve, either for servicing or day to day use. The servicing set-up procedure does involve a final verification of the instrument using a standard valve (originally supplied by Avo, but now no longer available), but only after all other adjustments have already been made.
Yes the advantage of the military Hickok designs (TV-3, TV7 TV 10 etc) is that no actual vacuum tube or "transconductance device" with a said to be "known transconductance" is needed to calibrate them. So the notion of a calibration valve is a redundant concept in the Hickok testing framework, in fact, using one to make any adjustments to the reading given on one of these testers would merely throw in a variable making the tester less accurate and less consistent with its fellow testers. (Which is also what these do on other testers too, if the problem is carefully considered). Needing a calibration valve for any valve tester is like saying a transistor hfe tester needs a "calibration transistor" when it simply requires calibration signals. Hickok appear to have figured this out, while others have not.

I'm not in entire agreement with the the notion about emission testing being a useful parameter and that transconductance is a factor not significantly affected by emission. One of the main reasons why manufacturers of valve testers chose transconductance as the main parameter to test, is that it falls as the emission falls and the valve ages. In fact, this was the basis behind many early signal control circuits where, to control the stage again, the filament or heater temperature was manipulated. An early Theremin being just one example of transconductance being manipulated by heater temperature.

A good "life test" would be to reduce the heater voltage by 10 or 20% and see if the valve still retained a reasonable transconductance and that would give some very rough indicator of how much practical life the valve might have left. However, as everybody knows, the exact future for any component might only be predicable with a crystal ball, because until it has happened, the future always remains uncertain.

Also, emission testing would likely be more useful for valves in switching and pulse application, TV deflection stages etc, where the peak currents were an important factor. For example reduced emission in a horizontal or vertical scan output valve shows up much more readily than the same valve operating in a Class A audio output stage and the raster scan on the CRT face gives a very good graph of it.

Last edited by Argus25; 18th Feb 2019 at 1:05 pm. Reason: add remark
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Old 24th Feb 2019, 2:46 am   #33
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Default Re: Valve Testers

Agreed, Argus25, there is no valve tester known to man capable of predicting the future health of valves with certainty, not even laboratory models.

I haven’t been able to unearth anything to bear out Gary Steinbaugh’s assertion, for reasons he gives, that emission tests are “a good test of a tube’s overall health”, though they do appear in an authoritative text like the Radiotronics book. But the following link seems to contain a good deal of sense about valve testers generally and the interpretation of their readings, particularly from the two mid-century trade articles given there.
http://www.tubesound.com/tube-testin...a-tube-tester/

My attention was particularly drawn to the articles on the Sencore range of Mighty Mite emission testers, of which many thousands were made and bought and which, in experienced hands, clearly did what was required of them, so not perhaps entirely useless toys then. The website author, Bob Putnak, clearly has quite a lot of time for them.
http://www.tubesound.com/sencore-mighty-mite/
http://www.tubesound.com/repair-cali...e-mighty-mite/

Another fan is at
file:///D:/Valves%20-%20Sencore%20MU140-MU150%20description.pdf (sorry, but I can't get this to display as a link, so cut and paste into browser)

For those persuaded by Mr Steinbaugh’s view, the following circuit (and manual) of the Sencore Mighty Mite VII could possibly form the basis of an emission tester for self construction, particularly since its pcb components are attractively simple. Elsewhere, it could be simplified further still by sacrificing the slide switches, substituting the valve pin numbered leads of the Australian baking tin tester, the “settings” so vital for speedy professional testing unnecessary for occasional amateur use. Also, the heater voltage choices could sensibly be reduced and the transformer secondary voltages substituted with whatever is suitably to hand, with appropriate circuit adjustments elsewhere.
file:///D:/Valves%20-%20Sencore%20TC162%20manual%20.pdf (sorry, but I can't get this to display as a link, so cut and paste into browser)

I appear to have answered my own question about the significance of the “emission” readings, at least for this particular circuit, since the fsd of the 1mA meter is given in arbitrary units of 120, the good/bad scale placed as indicated in the attached picture.

After very many years of producing just emission testers, and perhaps stimulated by developments in the products of their rivals, Sencore finally marketed the Continental at the top of their range, this offering, in addition to emission testing, a form of transconductance testing as well. Hmmm. Then, they stopped making valve testers altogether!
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Old 24th Feb 2019, 5:01 am   #34
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I had a look at this, he makes a big deal about voltage sag when the valve goes under test in Hickok testers.

But in the TV-10 at least, the line voltage master calibration control & metering is derived from the transformer secondary, so for heavy heater current valves its easily tweaked back to standard after the heater has warmed up and all voltages derived are from the one transformer and effectively re-calibrated. It is not a problem in the TV-10 tester, but he mentions all sorts of other Hickok units that I am not familiar with, so I can't really comment if they have a problem in that area, or not.

I think we both agree that valve testing has a limited but not zero utility value. Any test data obtained should be interpreted with caution.

I think the test is off to a better start if it can provide the user with direct transconductance data, to compare with the manufacturer's suggestions of what is an expect normal range (on that tester) for that part.

After that though, beauty is in the eye of the beholder and the data can be interpreted in a number of ways.
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Old 24th Feb 2019, 8:44 am   #35
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....... I could have added this remark, perhaps after a glass of Chardonnay to disinhibit the frontal lobes. Not to offend anybody, not the intention, but this is how I feel about it:

I expect that any test or measurement/apparatus should read out its final display in scientific units. For example an oil pressure gauge in pounds per square inch or Newtons per square meter, or an volt meter in Joules per Coulomb(volts) or an amp meter in Coulombs per second (Amps). Car manufacturers once decided that the punters wouldn't understand or care about monitoring the specifics, so they cooked up the notion of "idiot lights" or "good vs bad" indicators and trashed the real instruments.

I just can't put up with that and I don't regard any test equipment with a pass -fail output on it as being a "scientific instrument". Please don't be offended, it is just my opinion. So when I see the Green-Red good bad meters on valve testers, I just look the other way.
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Old 24th Feb 2019, 2:15 pm   #36
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Default Re: Valve Testers

Do you ever use a continuity tester? Surely that's a pass/fail indicator. Yes there are times when the resistance of a switch contact, fuse, or cable is worth measuring (in ohms). Most of the time you just need to know if it's conducting (below a certain resistance) or not. Idiot lights have their uses. Yes an oil pressure gauge on an engine is useful (and you can see if the oil pump, pressure relief valve, etc is behaving correctly by observing the pressure at various speeds). But a light that catches your eye and warns you there's almost no oil pressure and you'd better stop NOW to prevent bearing or piston damage is also useful.

Ever done a quick test on a transistor by checking the 2 junctions are still good as diodes? Sure it doesn't tell you if the transistor has signficant gain, but it weeds out the real duds with opens or shorts.

The valve tester I (occasionally) use (AVO VCM IV) has a pass/fail scale on the meter. But you can also use it to measure the mutal conductance of a valve in mA/V. And most of time I use it in the latter way actually.
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Old 24th Feb 2019, 3:59 pm   #37
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Default Re: Valve Testers

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Originally Posted by Argus25 View Post
I expect that any test or measurement/apparatus should read out its final display in scientific units. For example an oil pressure gauge in pounds per square inch or Newtons per square meter, or an volt meter in Joules per Coulomb(volts) or an amp meter in Coulombs per second (Amps).
I suspect it's worse here in Blighty than in the land of Aus, Hugo. Any physical quantities in the press have to be translated into double-decker buses, jumbo jets, or olympic swimming pools. Electrical units have to be converted into 'homes'

In the areas of science and engineering, most people are proud to not understand anything. Oddly, they can do arithmetic, but only in betting odds with a smaller group able to add up on payslips and bills.

It would be fun to make a replacement meter for valve testers with no numbers, just the words: "Strong, Very strong, Very Very strong, Awesome! and Stronger than Chuck Norris" written up the scale.

David
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Old 25th Feb 2019, 12:34 am   #38
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Do you ever use a continuity tester? Surely that's a pass/fail indicator.
Yes and I agree with your remarks. But a meter on a continuity check with its beeper is the most primitive of the meter's functions.

Surely in the case of a test instrument, like a valve tester, configured with multiple sockets, power supplies, metering etc, one would expect more from it than a heater continuity test, or just electrode shorts and pass -fail output.

It is actually a shame, when all the equipment required to compute and display a transconductance test result is already right there in the box in most testers, and the manufacturer chose to make a pass fail or good bad output as though the test was the result of a primitive function.

I think it was done because the testers were being used as a screening tool, intended to be operated by a person who might not be able to interpret the significance of transconductance data, so as to reject valves deemed by the tester as "duds" and throw them in the trash.

I can imagine one triode (maybe a 6J5) talking to another in the bottom of the trash can: "After I was made they found something wrong with me and threw me away like a piece of rubbish" Ignoring the fact that this triode might have been able to have a productive life in some application.
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Old 25th Feb 2019, 12:38 am   #39
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It would be fun to make a replacement meter for valve testers with no numbers, just the words: "Strong, Very strong, Very Very strong, Awesome! and Stronger than Chuck Norris" written up the scale.

David
Now that is what I call a well calibrated scale. I bet it would be a hot seller on ebay !
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Old 25th Feb 2019, 5:30 pm   #40
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Somewhere I have a pocket pass/fail valve heater checker. It's badged 'Eagle' so it's not home-made. It's a metal box about the size of a tobacco tin containing a pair of AA cells, a torch bulb and a limiting resistor (so it won't burn out D-series battery valves). There are a number of valveholder with the heater pins wired to said simple continuity tester. A B9A, pins 4 and 5. A pair of B7Gs one using pins 3 and 4 the other using 1 and 7 (that one is labelled 'for battery valves). An octal certainly with pins 2 and 7 used, I have an idea that pin 2 is linked to pin 8 to test certain rectifiers.

It is a very basic test but it weeds out the real duds.

As for 'pass/fail' meters on 'real' valve testers, as I said the AVO VCMs can be used to read mutual conductance, anode current, etc in 'real' units. Are there other models that can't be used like that?

And related to the sub-thread, I want a voltmeter with markings 'tingle' 'ouch' 'b***dy h**l' and 'sent to the hereafter' on it
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