I've developed an annoying hum when using the phono section of my RM5III preamp that's driving me bonkers. Sometimes I use just the phono pre section by using the tape out to another preamp, sometimes the phono & line stage of the RM5 together-no difference in hum level in either configuration. RM5 line stage is set for 9db. gain, cartridge is a Garrott Bros. Optim FGS with 4 mv. output. The VPI Scout table is grounded well to the ground of the RM5. I've just installed a new set of ultra low noise Amperex Orange Globes I bought from Andy @ Vintage Tube Services specifically for phono use, so I'm pretty sure that's not a factor. The hum sounds like a constant 60hz. kind of hum, not like tube noise. I've lifted grounds in the system, tried only phono with no other components or video, etc. hooked up, no change. I've tried different interconnects, no change. There's always been some slight hum with phono use, but it's definitely louder now than it's been in the past, very easily audible from 15 feet away from my speakers (87 db. efficient, no uber sensitive horns or anything.) I'm curious if an aged component somewhere in the circuit could be the culprit? Thanks in advance for any advice.
