I've been restoring a Philco 42-350. I've replaced the rotten rubber wires, all the wax caps and about 90% of the resistors. So the radio plays very well on all bans most of the time. But the push buttons and broadcast bans will randomly stop working. I can restart both bans by touching the plate (pin 2) of the XXL mixer tube with my voltage meter. This works every time and the radio will play normally (for awhile). Could this be a problem with the Mica caps or my Oscillator coil?
Did you rebuild the IF cans? There is a 4000 uuF mica capacitor inside the 1st IF that goes between the XXL plate and the band switch. You can probably test it if your meter has a capacitance function. If you didn't rebuild the cans, there might be some rotten wire that should be replaced.
When there is an intermittent problem that is solved by the touch of a meter, I usually suspect some unwanted capacitance somewhere, either because of an open resistor that normally bleeds off a charge, or because of a bad contact. Try cleaning the band switch and push-button switch block with something like deoxit. Double check your solder joints. Sometimes old wire will look like it has soldered, but really makes poor contact with the solder.
I actually have a similar problem with a 42-355 that I listen to almost daily. The push-button stations will suddenly go away but will come back when I push any of the other push buttons and then switch back to the station I was listening to. I cleaned the switches before I put the chassis back in the cabinet, but the problem developed not too long after. I haven't had a chance to take it apart yet because of other projects, but I'll do it soon.
Let us know what you find out, because it might be related to the problem with my radio.
I rebuild the other two IF cans. The wires on the one with the 4000 uuf cap were in very good shape so I had left it alone. So now I went ahead and changed out the 4000 uuf cap but no luck it didn't fix the problem. I plan on working on the solder joints next.
My problem turned out to be a couple of bad solders. I also broke the band switch trying to fix my first problem. I have finally fixed both problem just in the last two weeks.