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I have heard it for years and now I truly believe it .... the best tube tester is a working circuit.
I was trying to decide what to do with what I thought were dud 26 tubes that had tested quite a bit below minimum on my TV-10 tester. I had the tester gone through by the TV-7 & 10 guru out in Arizona when I first got it a while back, so I am fairly sure it is operating per specs.
Anyway... I decided to stick a pair of globe 26's that had tested at 500 and 550 (minimum being 750) in my 26 bread board. To my surprise they played very nicely and there was very little reduction in volume that I could hear. I proceeded to go through about 15 more tubes from the dud box and 10 of them worked just fine. The other 5 worked but had issues of noise, etc.
Bottom line for me is that from now on I will always do a final check in circuit on any tubes that test too weak as long as they don't show shorts or any other problems.
Edits: 08/26/15Follow Ups:
...I made this from S.Bench RAT design
Can measure loss of transconductance (= ageing) and Mu
For complete building, click the tread below
Nice work! How long did it take you to put it together?
The problem with testing in circuit is that you don't always have a reference. The tubes may "work", but how would you know if they could be better?
I have an old B&K,(Does not test 2A3 etc.) but it I am thinking about building the RAT or buying a uTracer kit to do more comprehensive testing.
I can never figure out how to buy that uTracer off the site though. I'm not sure if it available still or not.
I also considered just making a jig and kind of manually plotting the curves.
(I even considered building a jig that would mechanically draw my curves on paper with a pen.)
It will be one of my winter projects, I will watch your thread to see what you come up with.
Infamous sockpuppet
"I also considered just making a jig and kind of manually plotting the curves."
I qualify this aspect of tube performance in my own gear through distortion measurements. You'd be surprised how much difference there is from one tube to the next. It's a lot of work to match tubes this way, but worth it IMO.
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Buy Chinese. Bury freedom.
I'm thinking about trying this, too :-)
Vbr,
Sam
I would be interested in any details you care to share about your testing procedure.
I don't mind the time it may take as it would be primarily used on a few tubes for personal use.
Thanks!
Infamous sockpuppet
I use a PC soundcard (M-Audio 192 PCI) and ARTA demo software. I also built a small interface box to ease the task of switching between channels and setting input levels. If you search the archives, you'll find a good amount of information on this.
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Buy Chinese. Bury freedom.
I will look, it's a good thing I asked, I was just going to use some variable voltage sources and the scope.
Thanks.
Infamous sockpuppet
There have been quite a few posts by myself and member deathtube 667. We're both using the M-Audio card. At one time, I was shopping for an audio spectrum analyzer (HP) and distortion analyzer (Sound Technology), but then I tried this method. There are times when standalone test gear is more convenient, but I don't miss it in this case. I've dedicated a PC for this use, and the software lets me see everything I need to pick the best tubes from my stock. It also lets me optimize circuits in ways that would just be guesswork without it. IMO, there's no substitute for this capability.
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Buy Chinese. Bury freedom.
Right, I gotcha now.
I was thinking of just tracing curves, but you did mention distortion measurements.
That sounds even better, I will check it out.
Infamous sockpuppet
My feelings on that are if it sounds good it is good. Just look at it as another facet of tube rolling. There is no way to "measure" which particular tubes sound best to you except with your ears.
Edits: 08/27/15
Well, say you built a new amp and put in some used tubes, how would you know for sure if you are getting the best performance possible?
Sure the mid-range might sound good with some worn tubes, but perhaps you would have much better bass with a strong tested pair?
Only one way to find out.
Granted if you are already familiar with how a certain topology should sound, then your ears might be all that is necessary.
Infamous sockpuppet
Well first off, we would have to agree on what "best performance possible"means. : )
Ultimately I think your ears have to tell when the sound is the way you want it. Whether that matches any particular set of specs or not is not what matters to me. To some folks that matters more than anything else almost. Several of us have gone round and round here on whether it needs to measured or heard. Personally I think it has to be your ears, but there are others who think otherwise. That's why Heinz makes 57 varieties I guess.
I guess if we all thought the same we would all be listening to the same amp. : )
The problem with that is, Heinz only makes one Tomato Ketchup.
If you don't test it, you might inadvertently end up with Heinz "Heinz Cream of Oyster" or "Heinz Breakfast Wheat" on your hot dog.
You might then make inaccurate conclusions about the taste of your hot dog.
I can somewhat tell when tubes need changing by ear, but only if I have been listening to the particular amp over an extended period of time.
I am not saying your wrong, but for me in my DIY adventures I try to minimize the amount of variables when evaluating new to me designs.
No sense in throwing out good hot dogs because they sound bad with mystery sauce.
It's easier to make a conclusion of the hot dog's sound by using the original Ketchup.
The original Ketchup is thoroughly tested, that is why it pretty much tastes the same since 1896.
If you are not confused by now, you are probably hungry.
Infamous sockpuppet
I think a better analogy would be whether you want ketchup or relish on your dog. Testing will only tell you if one tube is different than another, it won't tell you which one you would like to listen to. For that you need them there ears.
I don't like relish, it's too hard to clean out from my ears. (:~o)
Infamous sockpuppet
what is the sound of one hot dog clapping? : )
I have without exaggeration, 100 or more 26 tubes that all tested low on my TV-7D/U, also calibrated by Dan. I saved them because I think the TV-7 has some problem with the 26 or they set the minimum too high as I rarely have one test good.
I don't know, but I never throw any "duds" away. It's mostly denial...I have thousands of duds from years of buying and selling tubes. I have so many $200-500 duds that I just don't want to believe are worthless *sigh*
I don't know how many Tung-Sol round plate 6SN7's that I have tested with plate imbalances to great to sell, but I bet it's at least 30.
"I KNOW you can hear it, but are you REALLY listening?"
I think it might be the low filament voltage, since it seems to be a problem on both the 7 and the 10 models. Or as you say the minimum might be set too high.
I'll bet if you test those duds in a working circuit you will find many of them are quite functional.
This little discovery has sure changed the way I will use my tube tester in the future.
Edits: 08/27/15
A working circuit is best, but not for the reason you've described. You've only demonstrated that a tube performing well below a new one can still amplify. The real reason to use a working circuit is that tubes that seem good in a tester will sometimes fail under the stress of actual use.
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Buy Chinese. Bury freedom.
I was having pairs of KT-88s going "red plate" on me and I could never be absolutely sure which one of the pair was defective (unless I witnessed arcing). I built up a simple circuit to power up the tube and bias it normally and ... Voila! ... I could find the culprits within a minute or two of being powered. And all this with no stress to my audio power amps.
Mike
Actually, the real reason is a combination of both things, with the end result being you know you have a tube that works in a real life situation.
Edits: 08/26/15
... a curve tracer.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Agreed...curve tracers establish the transfer function of the tube and are indispensable for determining how closely triode sections are balanced.
Vbr,
Sam
Not in my arsenal, never even seen one in action. Hard to come by aren't they?
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