my buddy never used the standby switch and now his amp/tubes are screwed up.  could that cause it?

i've got a tube amp too but i follow directions.

I've got quite a few tube amps, and the standby switch helps to prolong the life of the tubes.  A few don't even have a standby switch, but 95% do.

Eventually all tubes go bad, and can sometimes damage the amp in the process, but usually they don't.

Just make sure he replaces the tubes with tubes that have the proper bias setting, (the guitar store can make sure of this) or he can cause more damage just putting in new tubes without adjusting the bias of the amp to work with the new tubes.  

Mesa amps sells their tubes with a particular bias, and the amps are hardwired to run with this bias.  Fender has started doing this with a color coded scheme for their newer amps.  Otherwise, get a store tech to set the bias to match new tubes in before running it.

thank you sir.

the problem amp is a 5150 head.  i had one for a day a couple years ago but i wasn't satisfied so i returned it.

i have a mesa head and got a full set of extra tubes from the guy who sold it to me.  i've always wondered when you're supposed to change them.  amp sounds good so i havn't touched a thing.

Have your buddy test all the tubes in the amp.
He should have a complete backup set.
By substitution  he will be able to find the
weak tube. Other than that, if hes not a tech,
hell have to take it in to a tech for a
bench test. Hope this helps. Paul.