Quote:
Originally Posted by Electronic M
Tar.
The transformer is potted in tar inside that square black can. If the transformer gets hot enough the tar will melt and leak out ( it is also possible for it to chemically breakdown over the years and partially seep out).
Don't let the transformer run hot enough to melt the tar... That will kill it sooner or later. If the transformer runs hot your set is drawing excessive current. Could be from electrically leaky filter capacitors or a variety of other maladies.
If your set is recapped and working perfectly but the transformer is running hot and if that set uses 5U4 rectifiers you can remove them and replace with silicon rectifiers to remove several Watts of heater winding load.
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The CTC9 never used 5U4's, only a voltage doubler.
Also, the set was designed when the normal line voltage was between 115 to 120 volts. Now, most of the line voltages are running slightly above 120 volts so the transformer will run a little hotter.