My 5150 Combo broken?

[JohnHolland]

Hey Jerry, I was told that you were the god of all things 5150 over on metaltabs.com, and you're the first person I thought of to ask this question to. I know it does'nt have to do with amplifier modification at the moment, but it might later on. If you could answer this question I'd appreciate it very much.

I received my 5150 combo amplifier today via e-bay, and there's a bad problem. The actual volume output is significantly lower than it should be. With the pre gain on 10 ( lead channel ) and the post gain on seven on the 5150, my Marshall AVT50 combo is much, much louder. And this amplifier should be cracking the earth at pre gain 8 post gain 2. I think it might be a fuse that needs to be replaced, as I often hear that the stock fuses in these amps are pure crap. It may be a tube, a fuse, or a bad connection, speakers, or something. Either way, the tone sounds sort of thin and the volume is very low.

Does anyone know what the problem may be?

[Jerry P]

Hi John,
It's not a fuse. If the amp powers up, changes channels, and makes noise the fuses are fine. A fuse is either good or bad, there's no in between. If a fuse fails it failed for a reason, they don't go bad without help from something else. Fuses are there to protect the circuit.
As for your low volume try a different cord, try pluggin in an external speaker cabinet to rule out a speaker problem, different guitar, run it with no effects, etc. You wanna rule out all the basics first.
Then try a jumper cord in the effects loop and see if that helps your volume. The effects loop jacks can get dirty and cause low volume and cutting in and out. This would be my first guess from what you describe.
Could be a bad tube. You could swap in some different preamp tubes if you have any kicking around.
Jerry

[JohnHolland]

I've tried everything you've said, but no results. I'm thinking about unscrewing the circuit board to see if anything is loose.