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Posted:
Sun Mar 04, 2007 7:28 pmby Shannon Parks
1) Does it hum with the inputs shorted?
2) Are you using a three prong AC cord? Does it remove hum to use a cheater plug?
Alos, could you post a couple close up photos of the bottom wiring? That could help diagnose the prob.
Posted:
Mon Mar 05, 2007 7:51 amby TomMcNally
How is the hum when you have your preamp connected and the volume all the way down ? You really don't want to run a tube amp with no input, when testing, either short the inputs, or connect up a preamp. Open inputs are like antennas for hum.
If you're getting hum with the preamp connected, disconnect one input at a time until the hum goes away, then look for a ground issue. You'll almost always get hum when anything connected to TV Cable is connected, an almost always if a desktop PC is connected. There are ways to deal with this.
... tom
Posted:
Mon Mar 05, 2007 11:05 amby mesherm
I am betting that the transformers you replaced had a metal cover plate on the underside. The new ones do not and in your photo the input leads cross right over the power tranny, a sure invitation to pickup hum. Two solutions, buy a metal cover plate for the new trannies or reroute the input cables so they avoid the unshielded power tranny. Shielded cable will prevent capacitively coupled hum but not magnetically induced hum.
Mike