Udog, it sounds like it's a noise floor issue. Your DC likely isn't quiet enough so you are hearing some noise that it isn't filtering out. You have a few options, you can, if you know how to work on audio equipment without killing yourself, add smaller filter caps to bypass your current capacitors. .1 and .01uf may help. One common problem is the heater voltage, it's usually AC. If your amp is push-pull, than only the driver tubes on the input would need to be converted to DC, but AC uses less current as it's only putting out full voltage/current at the peaks of the sine waves, so while you can buy AC to DC converters on eBay, your transformer almost certainly can not sustain the higher current DC supplies, so you would have to buy another transformer just to run the DC which I believe uses 1.8 times the current AC uses, but just double it to be safe. I think 6SN7s use about 1.3 to 1.5 amps AC, so you would want a transformer that can supply about 3 amps per tube. Often that will cure your problem. Otherwise if it's really driving you crazy, a completely new power supply may be needed. Another option might be a new amp. Don Sachs makes an amp that puts out DC that is so quiet that the AC noise is in the micro volts, you can't hear that even with the most efficient speakers there are.
