60 cycle Hum Elimination in the Model 54
There
are several possibilities of hum in this model. One of these is leakage
from the "B" supply through the insulating material of the wire-wound
resistor to ground. Only the very first production [run] had any of this
trouble, which was corrected by replacing the resistor with the later type,
which was darker in appearance.
Any
wire insulation defects, particulaly where the wires pass over sharp metal
corners, can cause a hum, due to the grounding conditions which is established.
Grounded
resistors can produce a hum, which condition can also be produced by a defective
type 75 tube. [A filament to cathode short or leakage is common.]
From the Philco Serviceman - October, 1933.
