On my Philco model 635 when you turn it on it squeals real loud until it warms up for 2 or 3 minutes. Does this even with the phono switch in phono. Sounds like a real loud whistle. I have recapped the set and changed out the 42 and 75 but no difference. Also, rebuilt all of the block capacitors.

:On my Philco model 635 when you turn it on it squeals real loud until it warms up for 2 or 3 minutes. Does this even with the phono switch in phono. Sounds like a real loud whistle. I have recapped the set and changed out the 42 and 75 but no difference. Also, rebuilt all of the block capacitors.

This sounds like a job for Freeze Spray.
Lewis

::On my Philco model 635 when you turn it on it squeals real loud until it warms up for 2 or 3 minutes. Does this even with the phono switch in phono. Sounds like a real loud whistle. I have recapped the set and changed out the 42 and 75 but no difference. Also, rebuilt all of the block capacitors.
:
:
:This sounds like a job for Freeze Spray.

Well, thanks, but I didn't use freeze mist. What I discovered was that if I removed one end of a small wire going from where the wire that connects the cap of the 6A7 to just above one section of the tuning condenser to the just above the next section of the tuning condenser that the squealing almost completely stops and I get many more stations. There is still some squealing on weak stations at just a certain point in the volume control. Above or below that point the squeal stops. Reception is much better and
one end of the wire just dangles like a gimmick.

If all is proper with the radio, then it will work as originally intended. Thus freeze spray wouldn't uncover anything that inspection for originality wouldn't otherwise reveal.

Be sure that all RF and primary AF tube shields are in place. Be sure that small value caps from B+ to ground are in place and functional (wet electrolytics have a high power factor, and don't filter RF frequencies well, and so it is necessary to also have a small value paper cap in parallel to do the job and prevent RF from one stage from getting into another). Be sure that they are where they should be as shown on the schematic. With one radio I was working on, there was a .05 MFD cap going from RF B+ to B-. Between RF B+ and the primary B+ was a 100 ohm resistor. I accidently put the .05 MFD RF filter cap on the primary B+ side instead of the RF side, and the set went into squeels and howls. Simply moving the cap to the other side of the resistor made all of the difference.

Check for misplaced wires, incorrect connections, as well as grid and plate wires being too close to eachother. Keep the speaker wires away from all tubes (except the output) and the antenna wire.

T.

:If all is proper with the radio, then it will work as originally intended. Thus freeze spray wouldn't uncover anything that inspection for originality wouldn't otherwise reveal.
:
:Be sure that all RF and primary AF tube shields are in place. Be sure that small value caps from B+ to ground are in place and functional (wet electrolytics have a high power factor, and don't filter RF frequencies well, and so it is necessary to also have a small value paper cap in parallel to do the job and prevent RF from one stage from getting into another). Be sure that they are where they should be as shown on the schematic. With one radio I was working on, there was a .05 MFD cap going from RF B+ to B-. Between RF B+ and the primary B+ was a 100 ohm resistor. I accidently put the .05 MFD RF filter cap on the primary B+ side instead of the RF side, and the set went into squeels and howls. Simply moving the cap to the other side of the resistor made all of the difference.
:
:Check for misplaced wires, incorrect connections, as well as grid and plate wires being too close to eachother. Keep the speaker wires away from all tubes (except the output) and the antenna wire.
:
:T.

Originally, he said it squeals until it is warmed up. That is why I said to freeze it.
Lewis

Good point!

:Good point!

I found that the phon switch was open and that cured most of the squealing except now still does it a little when I turn the volume control which shows erratic readings with an ohmmeter but I guess not much cure for that unless I want to disable the tone circuits. No good way to replace the volume control without chucking the tone circuit.

I take it you are saying the volume and tone pot is a duel setup. You should be able to take it apart. Clean the disk, and adjust the wiper where it rides the disk if need be. May as well do the tone pot too while you have it out. No use to put up with a spotty volume control.

Should the volume control have permanent dead spots, patch with small amounts of window defogger repair paint (at automotive stores). Repairs must be small, as the paint has a very low resistance, and will create a flat spot.

Be sure that if you retension the wiper that it doesn't have too much pressure, and that no sharp edges contact the resistance material. Apply a thin film of dielectric grease (automotive stores) to the resistance material, as well as the wiper shaft.

Intermittant volume/tone controls can definitely cause squeeling, especially when the amplifier has a lot of gain and minimal shielding.

T.