I've been having a lot of trouble with my peavey 6505+ 112 combo ever since I got it. It randomly loses all its gain. I would switch out the pre amp tube closest to the back of the amp, and that would seem to do the trick for a little while, I had to do it several times. When that stopped working I took it to a local guitar shop and had their amp guy take a look at it. Apparently there was 2 lose pre amp sockets and a couple burnt capacitors. I picked it up yesterday and took it home without trying it. It sounded ok last night, but the gain seemed weak. I had the pre gain at noon and the post at 1.5-2. That amp should have more than enough gain, at those settings from what I've seen.

This morning I tried it and the gain had gotten even lower. I had the pre amp at 2 o'clock and still not much gain. So I took the preamp tube out of the socket closest to the back of the amp again, and reseated, and instantly got the 6505+ sound that we all know and love, sounded better than ever! It seem to me that the tube is not getting consistent contact with that particular socket. Before I took it to the amp guy, I tried electrical contact cleaner and as well as putting the tube in and out of the socket gently to make sure contact was maximized. Is there anything else I can do? It currently works fine now but I'm getting really sick of having to mess with this amp!
I've seen this problem a lot and it is because the solder joints on the pots and jacks can crack causing heat related changes. That's why it works for a while and then doesn't. This involves removing the amp circuit board and reflowing the solder joints on the pots and jacks.

It could be that removing and reinstalling the tubes is just flexing the circuit board enough to make it seem like that the problem is the tube. Of course this is only one possible diagnosis, but in my experience it's a very likely one.
Last edited by fly135 at Jul 16, 2013,