09-27-2014, 07:38 PM
Check the two 10 ohm filament shunt resistors (flex type). If one of these is open it will cause a hum.
These two resistors set the electrical center of the 2.5V filament winding which is referenced to ground. They perform the same function as a center tap of the filament winding. This is important because the 47 output tube has a directly heated filament, so to cancel hum the two filament pins must be balanced to ground.
These two resistors set the electrical center of the 2.5V filament winding which is referenced to ground. They perform the same function as a center tap of the filament winding. This is important because the 47 output tube has a directly heated filament, so to cancel hum the two filament pins must be balanced to ground.
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