hissing and humming vox ac15cc

[burning tires]

hello, I have an ac15cc It hisses a lot and hums when reverb is engaged. it is only a few years old and has seen minimal use. the only mods are, I removed the bright cap, and replaced the reverb tank with a better one. the hum was there before the tank upgrade and even with the tank disconnected. any ideas?
thank you

[Mars Amp Repair]

Is the upgraded tank of the same impedance? I could see where the return of the tank (out) would induce quite a bit of hum/noise if the impedance were radically mismatched with what was supposed to be there.

Hum from the tank since it was there with the old tank, could be induced by its proximity with the power transformer...yes, even if it is in the same original position. Weirder things have happened.

You might just remove the tank to get it away from the chassis & see if that quiets the hum down.

Also the original tank may have only grounded the shield side of the 'out' rca jack to the tanks chassis, be certain that the input side isn't also grounded to the chassis of the tank on the new tank. Some are wired this way with only the shield (gorund) of the input side to the tank chassis. From the schematic, only the out side should be grounded to the tank chassis.

Hope that helps a bit, if not a bit confusing...glen

[metalangst]

Yes, only three ends of the two tank leads should be grounded. confused? This is to prevent a ground loop while shielding both send and return. Also the tank may need to be in a sack. If there were any pads or boards on the old tank, they need to be on the new tank. Unscrew the tank and move it around while the amp is on to find the "sweet" spot, it may be as easy as loosening the screw, or adding rubber bushings.

[burning tires]

it hums the same with the new tank as the original. it also hums with the tank disconnected. the new tank sounds 1000x better than the one that came with it. but both have the same hum.