Thanks for the information. This confirm what I was thinking, some say that power tubes must be replaced after 2500-3000 hours, some other used a set of tubes much more than that time..
About turning of a tube amplifier when it does not play music, is it interresting to do that if the amplifier stay , for instance, 15 minutes playing nothing ? (I often read that power up an amplifier is not good for the power tubes so it is better to let it on if it doesn't work for a short time ...).
Christophe
Don't worry about short periods like 15 minutes. You can just leave the amp on.
Yes, as a general rule the heaters in tubes are more likely to fail at turnon, just like lightbulbs do.
However, there is also a finite amount of electrons that can be boiled off of the cathode before the coating wears out.
So you don't want to turn the equipment on and off too much, but you also don't want to just leave it on.
I tend to leave my system on if I'll be coming back in a few hours, but I'll turn it off if it's going to be longer than that.
Tubes are actually pretty sturdy. They were used in consumer radios and TVs for a long time, and they lasted quite well. They even lasted very well in car radios, and that's a harsh environment.
I just found an old GE "portable" AM radio, with a lead-acid battery and vibrator. I'm sure the caps are flaky or not working at all by this point, but I bet the tubes are fine.
I also fired up an old GE AM/Shortwave table radio and it still works. I bet it had been sitting for 25+ years. I used it a lot when I was around 9-11 and my parents used it a lot before that. The only things that burned out were the lightbulbs for the dial.
