FM Tuner Drift

[zeno]

My father also bought the same radio new. Was a fixture
in the house. Never broke, just cleaned the controls. My
brother uses it now.
Anyhows the drift is prob a bad tube. Start with any that are
FM only if the AM is OK. Tube will prob test leakage.
Then do the IF tubes. Filter can also a possability.
Drift is vague, describe better if you can.

This radio uses PTO in the FM for tuning, DO NOT mess with any
coils etc. PTO is only seen on the highest end communications
gear, I dont think anyone else used it at the consumer level.
Its a good example of balls out quality we used to make.
If you go to junk shops or flea market in these parts you
will see lots of them still working along with other 1950's
Zenith radios, rarely any other brands. They are damn near
immortal.

73 Zeno