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 Post subject: How to improve tube testing
PostPosted: Apr Wed 01, 2020 11:47 am 
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Some interesting discussions recently about better testing of tubes. What many of us are used to is the simple emission test, but some prefer to actually measure the transconductance, defined as the partial derivative of plate current with respect to grid voltage. Going beyond this, some may be interested in doing testing based on the quality of sound in tube-based equipment.
The secret is to measure sound at the source--i.e. in the tube. This can reveal a variety of issues, including defects in a cathode, or photonic impaction at the various grids.
In a perfect tube, the electron cloud dynamics are gaussian (the mathematician's way of saying "white noise". But, if there is a defect (eg imperfect plating of the emissive material), the noise spectrum will be altered. All that is required is a small microphone placed on the tube pin leading to the cathode. This is then connected to a spectrum analyzer, which will reveal any anomalies in spectral distribution. With multiple microphones, we will be able to perform the sonic equivalent of a CAT scan, giving is unprecedented insight into to subtleties of vacuum-tube performance.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 12:45 pm 
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I think if you can somehow add an output amplifier to your spectrum analyzer, you could probably hear the tube..... all those microphones should be worth something. ;-)

Make sure the output amplifier is tube based.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 12:53 pm 
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If anyone missed what Barry is trying to say:
If you want to know what a tube (or a cap, resistor, or any other device) sounds like, you have to listen to it

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 1:00 pm 
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It is important to perform this test in a dark room as photons can interfere. Also place a lead sheet over the entire apparatus to avoid Gama rays and micro meteor particles striking the elements.


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 1:11 pm 
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Good point!!
For more on Photonic Impaction, here is a good article:
https://www.nearbycafe.com/artandphoto/ ... al-memoir/
I still remember the original that came out 20 years ago....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 1:18 pm 
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Extending this logic one step further, the entire test apparatus, or even room, should be placed on a concrete slab at least 4' thick. 8' would be better. Subsonic vibrations could severely impact this test. I'd think some magnetic shielding UNDER the test equipment would also help shield the tube from the earth's magnetic fields, which might make the tube sound. .......magnetic, somehow. A few inches of lead should suffice, and also assist in the low frequency rumble problem.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 1:21 pm 
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Lou deGonzague wrote:
It is important to perform this test in a dark room as photons can interfere. Also place a lead sheet over the entire apparatus to avoid Gama rays and micro meteor particles striking the elements.


Exactly right. Einstein described the Photoelectric effect where photons eject electrons from metal surfaces, with a work function. This would alter the sound, though only perceptibly with classical music, its extremely difficult to detect with Heavy metal due to the frequency spectrum.

I think the operator also needs to be shielded with a good coat of aluminium foil, or preferably lead sheet wrapped around their head or the tube elements could absorb additional radiation from that source. This way it is more like a "double blind trial" where neither the experimenter nor the subject has any idea what they are doing, which is not only apt, but also a prerequisite for this experiment. And Gosh, what if the tubes being tested don't have black plates or square getters and are mismatched for their sonics. It might just cause a tear in the time-space continuum and transport the whole experiment back into the dark ages.


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 1:32 pm 
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Some really good points here---I hope that the right people read this thread....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 2:08 pm 
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My tube tester has a pair phone jacks for a headphone. Tap the tube with a cork hammer, done :D

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 3:02 pm 
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Chas wrote:
My tube tester has a pair phone jacks for a headphone. Tap the tube with a cork hammer, done :D

Do you have any idea what the penalty is for derailing a factual and proactive discussion???
microphonics is an old issue--hit the tube with one kind of hammer and you get the typical microphonic sounds. With a different hammer you get----wait for it----different sounds.
What I'm talking about is the more subtle sounds associated with---eg---the details of how the cathode is deposited and pre-conditioned using photonic digression......
Time to go: 14hours (EST).......maybe there will be a prize....;)

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 3:02 pm 
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I'm waiting for someone to report they did that.

No doubt you would need oxygen free copper to wire it up or the results would be invalidated.


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 3:40 pm 
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You are aware, of course, that the earth's magnetic field will interact with the electron cloud in the tube and change its distribution, thereby influencing the sonic results of the test. The test apparatus should be mounted on a turntable which spins opposite to the earth's rotation so as to cancel these effects. In order to take the readings the turntable needs to be big enough that the user can sit on it and rotate as well.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 3:56 pm 
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Quote:
is a small microphone placed on the tube pin leading to the cathode.

I am going to use a ceramic phono cartridge for the pickup device. I believe a magnetic pickup might disturb the local surrounding magnetic fields causing invalid readings.
This type of mechanically coupled pickup cannot be used in California due to the unpredictable seismic activity vibrations induced.
My methodology for verifying that this framework runs in X(n) time. This seems to hold in most cases. Rather than improving my sensor with networks, I chooses to harness Byzantine fault tolerance . I consider a heuristic consisting of X++3.78n access points. Any extensive analysis of scalable symmetries will clearly require that the foremost symbiotic algorithm for the construction of this tube virtual machine. This may or may not actually hold in reality. Obviously, the framework that my system uses is solidly grounded in reality.
which of course is necessary so that the famous stable algorithm for the refinement of the Turing machine by xLi is recursively enumerable.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 5:32 pm 
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Quote:
Obviously, the framework that my system uses is solidly grounded in reality.

.......as are we all .... But I fear that by grounding our reality, some of the space-charge may have been dissipated, or at the very least, deformed.

I've also been thinking that the very act of testing the tube, might change it, possibly forever. It's almost for certain that even thinking about testing it will cause the tube to change some of its characteristics. This is not unlike certain aspects of Quantum Mechanics (I think). I don't remember much about Quantum Mechanics, but I think the last guy who fixed my truck was one.

.....anyway .... once you test a tube using any of the various methods mentioned above, it will probably sound different anyway. I'm sure if you use a metal hammer rather than a cork one, it will SURELY make a different sound, be it ever so brief....

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Last edited by Barry H Bennett on Apr Wed 01, 2020 6:45 pm, edited 1 time in total.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Wed 01, 2020 5:41 pm 
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I have created a monster......

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 2:00 am 
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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. It's almost for certain that even thinking about testing it will cause the tube to change some of its characteristics. ...


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.

Even with multiple stages of buffering (IC's Fets, transistors, loose coupled coils) I could not get enough isolation so there was zero "measurable" effects on the L/O. A change at the output is always reflected back to the input of even a long string of buffers, detectable in this case, as a small frequency offset of the L/O, when the buffer output is shorted out.

(This is why of course the audiophiles know that their speakers will have some effect on the loading of the cartridge in the turntable, ultimately changing the dynamics there and amazingly, some can hear it, the level of auditory skill they have is astonishing)

In the end the only way I could get "apparent" isolation was to go for an optical coupling. Attached is a photo of a small module with an optical block inside the brass cube. It is a variation of Manhattan construction, except I used a brass plate rather than a pcb, and the pcb rectangles are soldered from the rear of the plate which has holes in it, then the excess solder is planed away. (You won't likely have seen this construction method elsewhere, I devised it for my own projects).

With optical isolation the loading effects are apparently not transferred back to the input...not measurable. They are still coupled by EM waves though and one wonders, by principles of Quantum mechanics and the "spooky" effect (coined by Mr Einstein) whether the interactions at the photo-transistor are in some way communicated back to the LED through particle entanglement.


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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 2:07 am 
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It's official. I've now got a headache. Particle enganglement? That sounds somehow X rated. I was OK with circles of confusion, but I get just all cloudy in the quantum realm.

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 2:13 am 
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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 4:02 am 
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Thanks to all for an entertaining fool's day----I just took in a turbo-encabulator for overhaul, so I'll be busy for a while.
Stay well....

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 Post subject: Re: How to improve tube testing
PostPosted: Apr Thu 02, 2020 4:10 am 
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pixellany wrote:
Thanks to all for an entertaining fool's day----I just took in a turbo-encabulator for overhaul, so I'll be busy for a while.
Stay well....


Got the manual for that turbo? I've been looking for one, but can only find it on picofiche. My microfiche machine just laughs. Not looking for paper (really, 11,231 pages, and 770 of them are probably labeled "This page intentionally left blank" ???)

Mine is serial number 0401, if that matters in revisions.

Edit: Never mind - you have an encabulator. Mine is an encaboverulator - shorter chassis with the cabover.

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