The ShadowMusic Web Community

G'day All,
I have an original '67 AC30 TB with no mods whtsoever done to it. Everything is original except for valve replacement. I have been giving it a good workout lately( It has been dormant for a few years) and find that it is getting a hum up when I turn up the bass knob, getting louder as I increase to full .
Any ideas of what may be causing this .??
Cheers
Tom
OZ

Electrolytic capacitor. If the hum increases when the bass control is increased then that points to a capacitor in the preamp cicuitry at an earlier point in the circuit than the bass control.

These capacitors don't last forever. They consist of a semi-liquid electrolyte between foil and paper layers. This electrolyte can dry out over time. If the amp is from 1967 you could give it a new lease of life by having all the electolytics changed (there are not many of them).

Ray

thanks a million Ray,
I will send it off to my amp man asap.
Cheers
Tom