Anybody tube smart?

[Farview]

Indeed you are correct. However, you could go an extra mile with the preamp tubes, they do not wear out as fast as the power tubes do. Also, if your amp is biased hotter (effects the tone and some prefer a hotter bias, as do I) your tubes do not last as long.

That really depends on the amp. The way I used to tell when it was time to retube was: when the tubes were new, i could get my sound with the presence at about 4 or 5. When I found myself turning the presence all the way up to get my sound, it was time for new tubes. There really is no point in putting off replacing the preamp tubes, they are the cheap ones. Anyway, if the inverter tube starts to go, it will kill the power tubes prematurely.
I always carried the last set of tube with me in case I needed them.