Can plate voltage and cathode current tell me how much life

[jcr1234]

I am going to purchase a bias probe type device. I understand that these are used to match power tubes, but can the information they give be interpreted to show how much life is left in a tube?

[PCollen]

I am going to purchase a bias probe type device. I understand that these are used to match power tubes, but can the information they give be interpreted to show how much life is left in a tube?

Yes...you could compare tubes of the same type to see if one (or more) is (are) stronger or weaker at a given bias voltage, and so determine if they are 'matched' or perhaps their life is fading. The latter condition would be a more difficult judgement call than the former, and often it is easier to determine sonically if tube life is ending than by checking bias. But the probe could be a useful addition to your tool-kit if used properly and you know how to interpret and utilize the info it would provide you.

[David Root]

Power tubes show very clear signs of aging. The most obvious is the state of the flashing around the getter(s). Bright silver = almost new. Blackish center with pinkish outline, little or no silver color left = close to done. In between w/lots of silver + pinkish surround is still OK. Just my experience.

Old power tubes finally die in multiple different ways.

[Jana]

"Old power tubes finally die in multiple different ways."

The most spectacular is when beer gets spilled on the tubes while they are energized and hot.

[passfan]

"Old power tubes finally die in multiple different ways."

The most spectacular is when beer gets spilled on the tubes while they are energized and hot.

Quit giving your amps beer. They sound funny and play horrible when they're drunk, Although they don't think so.

[David Root]

I've managed to avoid that one so far!

One recent one, an old RCA blackplate 6L6, would work fine for about 5 minutes or so, then it would simply stop conducting and shut everything down. I checked it in my Maximatcher and it did the same thing, so it now sits on the window shelf in my little tube cemetery, along with the other old blackplate that goes into current runaway and kicks out the Maximatcher at 120 mA.