03-11-2008, 03:16 PM
Thanks, planigan. I figure the problem must be in the local oscillator/mixer circuit because when the frequency shifts there is no reduction in volume, so the IF must be the same.
I've replaced most of the rubber-insulated wires. There are a few that are both hard to get to and still have supple insulation, so I didn't replace those. If I wiggle those wires I don't get the frequency shift effect. I've also replaced all of the capacitors associated with the oscillator circuit.
I can often get the frequency shift to happen if I wiggle the tuning condenser and sometimes if I only touch it, so I am focusing on that component as the problem. As you say, it may be affected by warm-up.
Does anyone know where to get replacement tuning condenser grommets for the 40-150? Renovated Radios has some grommets for Philco tuning condensers at this site http://www.renovatedradios.com/parts.html#rubber but at 7/8 inch, they seem way too big for this radio.
Also, can you use anything besides compressed air to blow out the tuning condensers? I've cleaned it as best I can. If I knew of a product that would clean it but not hurt anything I would try it.
By the way, I did replace the mixer tube and the RF amplifier tube. I thought that since the volume isn't affected by the frequency shift, the IF should be the same, so I didn't replace the IF amplifier, detector, or audio amplifier tubes. I think I have spares so I could replace all of the tubes just to see.
I've replaced most of the rubber-insulated wires. There are a few that are both hard to get to and still have supple insulation, so I didn't replace those. If I wiggle those wires I don't get the frequency shift effect. I've also replaced all of the capacitors associated with the oscillator circuit.
I can often get the frequency shift to happen if I wiggle the tuning condenser and sometimes if I only touch it, so I am focusing on that component as the problem. As you say, it may be affected by warm-up.
Does anyone know where to get replacement tuning condenser grommets for the 40-150? Renovated Radios has some grommets for Philco tuning condensers at this site http://www.renovatedradios.com/parts.html#rubber but at 7/8 inch, they seem way too big for this radio.
Also, can you use anything besides compressed air to blow out the tuning condensers? I've cleaned it as best I can. If I knew of a product that would clean it but not hurt anything I would try it.
By the way, I did replace the mixer tube and the RF amplifier tube. I thought that since the volume isn't affected by the frequency shift, the IF should be the same, so I didn't replace the IF amplifier, detector, or audio amplifier tubes. I think I have spares so I could replace all of the tubes just to see.
John Honeycutt
