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Hi all,
here's a tough one (for me, that is):
Blues Deluxe hums badly at power up (10Vpp at speaker out), then the hum slowly decreases. After 10-15 minutes only a couple 100mVpp (still too much).
1.) Tubes are new and tested good in other amps.
2.) All voltages on all tubes very close to schematic.
3.) Pulling the PI kills the hum completely. New tube: No difference.
4.) Preamp out signal is clean without hum.
5.) Otherwise, Amp works normal and puts out 40W undistorted (when the hum is gone)
6.) Putting a shorted plug into the power amp in does not change the hum.
7.) Filter caps are new (same thing with the old caps).
8.) None of the controls do any change of hum.
Any ideas where to look next?
What am I missing?
Thanks in advance
Albert
here's a tough one (for me, that is):
Blues Deluxe hums badly at power up (10Vpp at speaker out), then the hum slowly decreases. After 10-15 minutes only a couple 100mVpp (still too much).
1.) Tubes are new and tested good in other amps.
2.) All voltages on all tubes very close to schematic.
3.) Pulling the PI kills the hum completely. New tube: No difference.
4.) Preamp out signal is clean without hum.
5.) Otherwise, Amp works normal and puts out 40W undistorted (when the hum is gone)
6.) Putting a shorted plug into the power amp in does not change the hum.
7.) Filter caps are new (same thing with the old caps).
8.) None of the controls do any change of hum.
Any ideas where to look next?
What am I missing?
Thanks in advance
Albert
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