I recently bought a broken Peavey Triumph 120 as my first attempt at amp repair. After replacing the fuses and tubes, I had sound for about five minutes until it died out and the tubes stopped glowing. The indicator light still worked though. I took the tubes out, put the amp back together and I had sound, and played for a solid 15 minutes. This morning, I went to turn it on and the tubes wouldn't power up again. I did the same thing but the tubes haven't lit up yet. Does anyone have any idea what could be wrong? The preamps (which I didn't replace) are definitely old and starting to turn white, but would that cause the power tubes not to turn on?