How can you tell if I need a new tube if not by listening?

Thank you,

I see nobody has responded to what I feel is a very good question. As someone who has owned primarily vacuum tube amplifiers through the years I have still not determined how to tell when the tubes, especially the output tubes, need to be replaced (yes, when they explode). Tube gurus with whom I have discussed this with have mentioned that if the parameters are grossly within normal range then the best test is "your ears".

Case in point, I recently changed out the output tubes in my Sophia SET amplifier because they were approximately 8 years old. The tubes are 207's, which are a 300B variant, so they are expensive and BIG. I can honestly say I noticed no difference in the sound, this with very revealing horn speakers. Thus one comes to the conclusion if the amplifer is well designed such that the tubes are driven conservatively, perhaps they can be expected to last decades. Indeed the driver tubes in my amplifier are NOS telefunken EL34s made in 1954 (with the metal base-supposedly made by the German military and sold to the Russians for use in their missile guidance system). I have decided not to replace them any time soon as the whole system sounds fine to me.

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Hi,You should check/test them every year if you are not experiencing any sound difference from before.Output tubes must be matched in plate current if you are using PP.

Well, the obvious signs are no glow in the tube, or static, popping or sizzling sounds

When in doubt, get the tube(s) measured on a (calibrated) tube tester.

One thing that can quickly determine the relative "health" of the output tubes, is to have the bias checked. If the tube won't bias right, then it needs to be changed, regardless.

This is something that should be done on a semi-regular basis- if you don't use the amp much, then maybe once every couple years- but if it's every day, you might need to do it once a year or more.

Preamp/input tubes don't generally wear out or fail catestrophically like output tubes can. It's not unusual to get decades out of smaller tubes. However, anything can fail randomly- however, with those, it WOULD either require testing the tubes, or a careful critical listening test while swapping new ones, to tell if any of those are out of sorts.

Regards,
Gordon.

Other than obvious new noises like hiss, crackle, pop or ringing, an old set of tubes will lose dynamics and sparkle. When they are worn out they just sound flat. When that is noticed, get them tested.

When they stop glowing.