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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 6:24 am 
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"This is an age old problem, how to test or acquire data from a system, without modifying the system you are testing. In electronics we go for high impedance, low capacitance scope probes & meters etc. In essence its the Heisenberg Uncertainty Principle."
Aaah, no, it's the schrödinger's cat dilemma. Simple solution; use a bigger hammer on the tube.
73,
-marc


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 10:09 pm 
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Yep. If it breaks, you KNOW it's defective, although I suggest that once you have let all the vacuum out, there shouldn't be any doubt. I also maintain that getting a bigger hammer may be a suboptimal solution.

For a while in my Army days (I was a firecontrol tech at the time), I had a track bar (think hefty, 5 foot long crowbar used to assemble and disassemble tank tracks) labeled "Coarse Alignment Tool" and a 16 pound sledgehammer labeled "Fine Alignment Tool".

John


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 10:12 pm 
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interesting .... I've been using "16lb sledge" in many of my posts for decades now, as the final alignment tool when all else fails. Sadly, I've never actually tried it at home ....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Fri 03, 2020 1:33 am 
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In the spirit of this April 1st post :lol:

My Dad had a unique way to test tubes.

"Throw 'em, if they pop, they're good..."

Chas

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 1:25 am 
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mbruvry wrote:
"This is an age old problem, how to test or acquire data from a system, without modifying the system you are testing. In electronics we go for high impedance, low capacitance scope probes & meters etc. In essence its the Heisenberg Uncertainty Principle."
Aaah, no, it's the schrödinger's cat dilemma. Simple solution; use a bigger hammer on the tube.
73,
-marc


Actually the Cat dilemma was that you could prove the cat was both dead and alive.

The Heisenberg principle relates to measuring a system, take a particle, the more data you acquire from it, say its momentum, the less you know about other aspects of it, say its position, because you have altered it by testing it.

From Wikipedia:
Introduced first in 1927, by the German physicist Werner Heisenberg, the uncertainty principle states that the more precisely the position of some particle is determined, the less precisely its momentum can be predicted from initial conditions, and vice versa.[2]

And of course when we make a measurement in electronics, we disturb the system we are measuring and alter it, this is why high Z input impedance FET probes were invented.

But of course these disturbances, most of the time in the TV's and radios we repair are of trivial significance.

I'm trying to figure out how the Cat fits in here and it just dawned on me. Schrödinger's Cat, is the contents of an Electrolyic Capacitor, because it can simultaneously be shiny and brand new, but be rubbish all at the same time. When you cut these open, despite the fact they can look good on the outside and measure ok, inside you can find all sorts of horrible corrosion going on in that "box". My advice, don't look inside the electrolytic capacitor, or that bad outcome you find there will then become set in stone.


Last edited by ACORNVALVE on Apr Sat 04, 2020 1:39 am, edited 1 time in total.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 1:34 am 
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We are all familiar with the idea that once you let the smoke out of something, it takes herculean effort to get it filled back up and sealed. It occurs to me that, in the audiophile world, there may be a startling correlary (I first used the word 'shocking' here, but changed it for obvious reasons).

At any rate, it is possible that once you cut open a capacitor, as noted above, you may let the SOUND out of it. No audiophile would ever accept that the sound, once thusly released, can ever be properly replaced.

I'll move on now, since the thread is wandering far afield from tube tester improvements.... maybe we should start another on improvements to testing audio capacitors ? That sounds odd to me....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 2:00 am 
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Sort of back to the OT, and (just a bit) seriously, I wonder if one could use a starved cathode approach in testing. The initial onset of electron emission would occur only on those tiny spots on the cathode that were most active. The rapidity of onset (the steepness of the curve) as cathode temperature is gradually increased might give some faint clue as to the uniformity of the cathode coating. Not necessarily good for cathode health, because there would be no space charge to protect the cathode, so this sort of measurement would need to be done gently. Or maybe I'm deluding myself?
R/ John


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 2:10 am 
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The first post is not far from wrong if it could be economically implemented in a device, the next level would be achieved.


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 10:15 am 
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Brobertson, I give you points for tenacity. :). NO test is ever going to be able to tell you how a given tube will sound in a given circuit. The very concept of how something 'sounds' is so subjective and individual as to render testing for such, useless. :)

But, it may sell on Ebay! :roll:

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 12:01 pm 
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Do you guys realize the penalty for turning an April Fool's joke into a serious discussion?

Quote:
The first post is not far from wrong
It's as wrong as I could make it. Sorry to disappoint--I'll try harder next year.....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 3:47 pm 
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Barry H Bennett wrote:
I've also been thinking that the very act of testing the tube, might change it, possibly forever.


Image


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 5:39 pm 
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pixellany wrote:
Do you guys realize the penalty for turning an April Fool's joke into a serious discussion?

It's as wrong as I could make it. Sorry to disappoint--I'll try harder next year.....


I almost believed it up to this point: ..."All that is required is a small microphone placed on the tube pin leading to the cathode."
Please be careful in choosing your words to be more credible next year.
Nice try anyway...


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 6:05 pm 
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We really missed a golden opportunity here.... along with the microphone, perhaps a tiny piezoelectric strain gauge could be fitted? That way you could really check the stress that those low bass notes put on your basic audio tubus.

One additional strain gauge might also be attached to a wrist strap, and worn by the tube tester operator .....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 6:10 pm 
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Since measurement inherently disturbs the system it follows that the only true measurement can be made by making NO CONNECTION to the tube elements. Only in this manner can we be confident that the measurement is not compromised.

I think this is more important than using oxygen free wiring in the test circuit.

As far as the cat metaphor goes, how can you tell if there's vacuum in a tube without breaking it open?


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 6:17 pm 
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Quote:
As far as the cat metaphor goes, how can you tell if there's vacuum in a tube without breaking it open?

Reminds me once again of the legendary flash bulb tester ..... hook it up... POOF!.... yup, that one was good ....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 7:36 pm 
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Tubologic wrote:
Please be careful in choosing your words to be more credible next year.
Nice try anyway...

?? Do you mean that I should make it more obvious that it's a joke??---that's no fun.
I'm going to assume that the challenge for next year is to make a better joke---i.e. something appearing to be more credible, and yet even more absurd

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sat 04, 2020 7:57 pm 
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ACORNVALVE wrote:
This is an age old problem, how to test or acquire data from a system, without modifying the system you are testing. In electronics we go for high impedance, low capacitance scope probes & meters etc. In essence its the Heisenberg Uncertainty Principle.

Some years ago I was making buffers to exit the L/O signal from some communications radios to an external counter. The task was to make a buffer that could monitor the radio's L/O without pulling the L/O at all, even if the buffer output was loaded, had a change in load impedance, or was shorted out.
I'm working on a setup to accurately measure the local oscillator frequency in the tube-type radios I'm restoring.

I'm doing this because I have some vintage AM broadcast band radios which drift up to 5kHz during warmup. Therefore the radio doesn't sound very good for the first 5 minutes after switching it on. These radios are AA5, AA6, or something similar.

What's interesting to me is that the circuit design for the AA5 radio is nearly standardized, yet I have some radios with extreme warmup drift and other radios with no drift at all. The amount of drift appears to be "model specific" so I am thinking there is something about either chassis layout or specifically the oscillator coils themselves.

I discovered that an x10 'scope probe can be connected to the cathode of a typical 12BE6 or 12SA7 converter circuit with only a +/-250Hz offset of the LO frequency. This can be reduced to +/-50Hz by adding a 4.7k ohm series isolation resistor. I have a very good frequency counter with a front-end which triggers reliably from the 1/10 signal amplitude provided by the x10 'scope probe. This is both simple enough and accurate enough as far as I am concerned.

Except for testing for large amounts shorts/gas and for very low emission, I've haven't found tube testers to be especially useful for checking converter tubes in AM broadcast band radios. It seems to be far more useful to substitute a "known to be good" tube when diagnosing problems in the local oscillator and converter. And for diagnosing the "warmup drift" issue, I'm thinking "in-circuit' testing is the only feasible way to understand and fix this issue.

-EB

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Sun 05, 2020 10:09 am 
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The answer is evanescent coupling (and a good stiff drink). :D
R/ John


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