I replaced the tubes in my Classic 30 last year, and now the sound is dying again. When i am playing, the sound suddenly becomes very quiet, and 10 seconds or so later, it will come back. When my amp is on, my power tubes light up, but none of my 3 preamp tubes light up. do i need to replace all of them? or what else should i do?
Gibson Vintage Mahogany LP
Line 6 Echo Park
Peavey Classic 30
Seagull Entourage Mini Jumbo
Vox V847A Wahwah pedal
i would suggest you should have a tech look at it... if you're preamp tubes aren't lighting up its either because they are burned out or the power isn't getting to them. In either cause there may be an underlying problem in the circuit, like a blown fuse or something that might be the root cause, so if you replace all the tubes it might just blow on you again
Peavey 6505+ w/ BG412F
B.C rich platinum pro w/ EMG 81&85
please check the lighter circuit. maybe the film circuit is broken
turn all the lights out and verify that the preamp tubes have no visible light.

power tubes do go bad, even after a year, under certain circumstances.

i agree with taking it in so +1 to all the other advice

(If it were me I'd check the bias measurment off the power tubes and compare that to spec)