Sunn Colloseum 300 making strange sounds

[AMPS]

Hello,
My colloseum makes strange noises when first turned on. without any instrument plugged into it the amp makes what sounds like an osillating feedback loop. i can control the pitch of the sound by turning the crossover knob. usually this sound stops after a few minutes but sometimes requires hiting the top of the amp in the center, to make the full bass signal come through.

i have opened it up. cleaned it out. checked all fuses. and all plugs are secure. nothing obvious is going on.

any ideas?

thanks.

[Don T.]

Hello:
 Sounds like broken solder joints to me. Do a real close check of the circuit boards and look at all the solder joints. They can look normal until a close inspection shows a near invisible ring around the solder where it has wicked up the component lead. That ring is actually a crack in the solder that makes and breaks connection or just adds resistance causing oscillations. They can be thermally reactive as the board and components expand and contract. Hitting the amp, of course, moves the board also. Just touch up any joints you have a doubt about. Potentiometer terminals are what hold the board into the chassis so they break most often.
Don T.

[AMPS]

Thanks!
I will give it a close inspection for broken solder connections.