Pv 5150

[pjgetz]

Hi there this is my first post but have been an avid reader of the site for a while. I've been trying to find the answer to my problem I'm having with my 5150 head. The preamp gain control controls the overall volume of the amp post gain control has little or no effect. The preamp gain control also cretaes a very ugly sounding metallic distortion. This happens on both channels. plugging another preamp into the return effects loop works perfectly.Just wondering what are some thoughts on this problem? Thanks in advance, Paul

[loudthud]

What's the history of the amp and general condition? Those amps have a mute circuit that is activated briefly when you switch channels. It could be bad. Have you tried swapping tubes around?

[pjgetz]

History of the amp is, it is well used. Have swapped tubes and I will verified pin voltages and post late today. The problem is weird it isn't intermittent. I think the pots are chnging the dc voltage in the amp somehow? Is it possible? What could cause that?

[loudthud]

Dc on pots is usually a leaky capacitor which isn't blocking DC. This will usually show up when tube pin voltages are checked. Broken solder joints between components and PC boards can sometimes work for years and then go intermittent or open once enough corrosion occurs. Do you have a schematic with PCB layouts?