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I realize that "noise" and "hum" are default complaints, but I am having trouble with a low frequency hum in a 1959 Marshall from 1971. I will do my best to describe it.
1. Both channels.
2. Instrument or no instrument.
3. No hum in stand by.
4. Starts when either volume gets to 5
5. No hum if I pull V2 or V3. Tried many different tubes in those spots and the hum is consistent.
6. No hum if I pull the power tubes. Installed a different quad of power tubes, and it still has the same hum.
7. All of the e-caps have been changed.
8. Have fooled around with lead dress and tapping on all the components. There was no improvement/discovery from that.
9. Plate voltage is right about 500 all the way across. Current is also very consistent at 33MA.
Any ideas about how to quiet this down a little?
Thank You
1. Both channels.
2. Instrument or no instrument.
3. No hum in stand by.
4. Starts when either volume gets to 5
5. No hum if I pull V2 or V3. Tried many different tubes in those spots and the hum is consistent.
6. No hum if I pull the power tubes. Installed a different quad of power tubes, and it still has the same hum.
7. All of the e-caps have been changed.
8. Have fooled around with lead dress and tapping on all the components. There was no improvement/discovery from that.
9. Plate voltage is right about 500 all the way across. Current is also very consistent at 33MA.
Any ideas about how to quiet this down a little?
Thank You