RD50 head from 82.It has a slight fuzzy sound in the background similar to a blown speaker.This sound occurs on both channels.Reverb and footswitch are disconnected.Have tried different speakers and output tubes with the same result.I realize I am not a tech and do not own any test equipment except a DVM.That being said,All voltages on the schematic seem close
Pin 3-611v
Pin 4-305v
Pin 5-20v[should be 30v?]
R64-16.26/7.46v
R67- -16.42/-7.6v
R62-40v/20v[should only be dropping 10v?]
so,could the D9 zener be at fault?
thanks,
Doug
D9 Bad
Yes. Voltage at D9 should be 30V. Zeners get "soft" as they age so change it out. Zeners also get hot so replace with higher wattage value and stand it off the motherboard 2mm for better heat dissipation. Good luck. -mgriffin
replaced D9.Works!
I now have 32v at D9.Background "fizz" is gone.Amp has more fidelity and power now.Thanks, mgriffin,for your help!
Doug