Vacuum Tube Rejuvenatiion
 

A few months I took up vacuum tube regeneration following the procedures recommended by Lane S. Upton, published by the California Historical Radio Society in 1978. I had a few "bad" tubes which I would have eventually discarded, but I never got around to it. I'm sure most of you are familiar with this--the rejuvenation process differs for different types of filaments and involves a voltages ranging from 100% to 300% of normal and times ranging from a few seconds to several hours. I accidentally killed one low-value tube, but had some success with several others. Notably, I moved a 45 from "bad" to "useful" according to transconductance.

After screwing up a few times, I put together a rejuvenation kit to use with my Heathkit TT-1. First, I made separate templates for each common filament voltage to show switch positions for the recommended rejuvenation voltages.

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I bought an automatic shut-off countdown timer because I'm forgetful. Also, for tubes (like this '01A) for which plate and grid voltage is not wanted, I made reusable filament pin extenders.

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My greatest difficulty is determining what type of filament each tube had. Upton gives a few examples and describes what the different filaments look like at rated voltage--"white" for pure tungsten, "orange-to-yellow" for thoriated, and "dull red" for oxide emitters. I can ignore the pure tungsten description, because I don't got any of those. But I'm never sure about the appearance of the thoriated and oxide filaments. Also many tubes, like all of my '99s, and so getter-coated that I can't see the filament. Here's a '26 which should be a "dull red" oxide emitter:

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I would call that a "non-dull orange-red."

So, putting together all the information I could find--published lists/examples and tube data sheets--I made a chart.

PURE TUNGSTEN: '01, 200
THORIATED: '01A, '20, '99, 200A, 210
OXIDE: '26, '27, 41, 42, '71A, 75, 78, 80, 7A4
These I presume are oxide emitters: '24, 57, 58, 76, 77, 84, 89.

Does this look accurate? I'd love to see a definitive list or filament reference for all pre-WWII globes and STs, but this is the best I cab do so far. Any other suggestions for being sure of filament type?

One other question: When a data sheet says "coated filament," does that mean oxide-coated?

Thanks,
Henry, The Eternal Novice.

I read regeneration and expected radio recievers using positive RF feedback for more signal gain, not tube rejuvenation.

Still interesting though. Some 20s tubes that I didn't want to pay to replace I've tried similar with, only it was full manual. I'd just increase heater a click or two till it showed gradual improvement, once it stopped I'd drop it to normal let it cool a moment and recheck.

OOPS. Regeneration? I misspoke. Sorry to disappoint.

Do you also monitor the heater voltage with a meter? I suspect that the “set to arrow” method would not yield consistent voltages if the current drawn by the tube heater varies from one tube to the next.

jr

Hadn't thought of that. The tubes I was working with ranged from .06A to 1.5A. I'll have to check that out and make templates for each filament voltage/current combination. Thanks.

:D Undead Zombie tubes for the Halloween season , I love it , great job Henry :thmbsp: