On 2023-02-08 03:31, Nigel Pugh wrote:
I can see this chat has been going on for a while, but unfortunately this is the only one I have read.
Worth mentioning, but I have a 532 amp and had hum exactly as you have described. The problem turned out to be the bakelite remote volume socket and blanking plug. That was conducting to ground. I never used it anyway so I bypassed it and the hum disappeared. Apologies if this has already been mentioned, cheap and easy fix, worth a try.
No, that has not been mentioned in this thread. It was mentioned when I first posted several years ago. I think it was Wesley Dean that mentioned this and that it is likely caused by rodent urine. I don't have that problem and I did wire the volume control to bypass that connector at some point. I did see this mentioned somewhere else where as well so it does seem to be a common problem. I really do think I have this narrowed down to a ground loop problem with the circuit for the 6AU6. I'd have to look and trace out the grounds in this area, but I think I can fly a couple of the existing jumper wires and isolate the ground and apply a new ground wire to the copper strap.
Carl Haines