Re: Need Help With 5150 Problem.
Wiggle the cord near the input jack and speaker jack, to see if it shorts out or keeps it's signal. It's possible that the cord was dangling in a way that cut your signal.
Buy a few cheap 12AX7's to keep as spares. Anytime you have a problem, swap out a few pre tubes to see if the amp comes back to life. I blew a preamp tube 2 days ago and the amp just made a grumbling noise till I put a new one in.
It's a good idea to turn on standby anytime you unplug your guitar and leave the amp for a few minutes. It's not good for it to sit idle with no guitar plugged in while running.