Listening for tube degradation

I agree with Eldartford, most often tube performance deteriorates slowly. Some can last a year while others may survive 20 years. Too many variables about circuit application, user care, etc. so time alone cannot be the measure.

I believe anyone with more than say 2-3 tubes in their system should try to find a tube tester and learn to use it. I'm not knowledgeable about electronics but I found a B&K tester at a swap meet and bought the tube charts and calibration instructions from them. That was a few years ago but the $ and effort paid for itself many times over.

Hitman and Larry:

As I stated earlier, I'm not an expert in electronics but I do believe an inexpensive tube tester can be a great value to most hobbyists with any tube gear. B&K and Hickock both made a number of good testers that can be found in the used market. I got a B&K 707 which, with the added Instruction Manual (including simple calibration instructions) and tube charts, cost me about $25.

The key is mutual conductance testing. I don't simply rely on "Replace" readings for tests but I record the Gm reading directly on new tubes (with a Sharpie), then note changes after a period of use. In general, I've been confident with readings within 15% of the new test.

For anyone playing their system on a regular schedule like Newbee, estimating hours of play can be relatively easy to indicate time for replacement. My listening is much more erratic so estimating hours of play for me would be a real WAG.

If you have a simple circuit with only one or two tubes it may be easier to simply replace periodically or have a dealer test them for you. Otherwise, for a sense of involvement with your system, find an inexpensive tester and learn to do it yourself.