Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: kagliostro on August 02, 2011, 03:42:48 pm
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Someone I encountered at a flea market told me that is possible to use a CRTs regenerator to regenerate old tubes
does someone knows if this is a real possibility ? :w2: ?
Thanks
Kagliostro
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TV CRT has extra problems. The cathode emitting surface must be small and on the end. Also cost was a big problem.
It sometimes happened that the CRT emission would fall off before the TV became obsolete. Not to zero, just too low for a good picture.
A new CRT would fix this. But a new CRT (part and labor) cost more than a new TV, more than most folks had in hand.
If the cathode is 90% dead, you can use-up that last 10% in 5% of the time by running the heater hotter. Like if you are drinking, and are getting low on money, drink faster.
The TV -will- go dead-dark sooner. However the "rejuvenator" was about 5% of the cost of a CRT job or a new TV. A price most people had handy. The repair person could sell it now, warn that the TV was going to die soon, let the customer start saving for a new TV.
There were a couple other TV rejuventors. Loose particles inside the CRT could short-out the close-space electrodes. I've "fixed" a couple CRTs by putting them face-down and beating the crud out (it falls to the screen, then down to the bottom of the bottle, harmlessly). There were also "zappers" to put large electric charge across pins to burn-out loose bits.
All of these were desperate attempts to avoid a $400 expense, in days when $400 would buy a very nice used car. Our tubes are much cheaper, and 6L6 or EL34 are cheaper today (adjusted for inflation) than they ever were.
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Thanks PRR for your explanation
The question now is
as the new TV use new screens the CRT regenerator is not more useful for the TV repair and may be is possible to get it on the cheap
yes, our tubes are much more cheap than CRT, but technically speaking the use of a CRT regenerator on a 12ax7 or 6v6 or ..... others, can give some positive effect and renew (for what is possible) also audio tubes ?
Kagliostro
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I wouldn't think so.
There are other tricks. When are your output tubes really dead? I've never had one that stopped making/passing sound. I have had 1 output tube that had an internal short. Other than that, I can't point to a real need to swap them (I don't have my amp on/operating many hours a day, every day).
When is a 12AX7 dead? Sure, some will have higher gain than others. As the tube ages, it doesn't die immediately, but the internal resistance rises, and observed amplification drops. You might not use it in a signal stage, but it would probably work fine in most tremolo oscillator circuits.
Something to think about. It's why even the best old tube testers stated in their manuals, "... the best test of a tube is to place it in the circuit."
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Thanks HBP
nothing to do with a damaged tube (as a shorted one)
only considering aged tubes where oxyde surface is corrupted in some way ........
When is a 12AX7 dead? Sure, some will have higher gain than others. As the tube ages, it doesn't die immediately, but the internal resistance rises, and observed amplification drops. You might not use it in a signal stage, but it would probably work fine in most tremolo oscillator circuits.
is an interesting point of view, you're right one tube can be useful in a different circuit
but what about power tubes ?
I was thinking about those tubes more than preamp tubes
reading your and PRR answer I think that if the CRT regenerator, especially those that acts this way
Submit a cathode ray tube regeneration by the technique of resonance, it means virtually stranded on the action starts and stops with the applicants and provide the grid with variable pulse trains of square waves at different frequencies, by setting in advance the maximum current that can flow in circuit and in any case should not exceed 100 mA maximum.
is disposable, not to be purchased specifically, a tray can be given, otherway the game would not be worth the candle
Thanks
Kagliostro
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is an interesting point of view, you're right one tube can be useful in a different circuit
but what about power tubes ?
That's the first point I was making. In 20 years, I have never had a set of output tubes stop working altogether, just from age.
Will they eventually age? Sure. When they do, they will most likely lose Gm, which means they will require a larger input signal for the same output current (and therefore voltage) swing. They will put out less power.
I argue that most of us do not need to produce a specific amount of output power, as a lot of us hobbyists most often play at home. So, as long as the tubes function (even weakly), they are doing the job. At least, that's how I look at it.
You could use the rejuvenator. But as PRR said, you do not get something for nothing. You get a somewhat improved performance now, at the expense of certain death sooner.
You probably don't need to buy the CRT rejuvenator. How do most rejuvenators work? The filament is operated at a higher than normal voltage for some period of time (say, 8-12v on a 6.3v filament). The higher voltage results in higher filament current/power, and heats the cathode more than normal. That results in more emission from the cathode than would otherwise happen at normal filament power. Sometimes, if the cathode isn't completely dead, the cathode will have increased emission after you switch back to normal filament power.
But the boost probably won't last long.
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Many thanks for your answer
Kagliostro