04-05-2024, 10:54 AM
The Riders/Philco provided schematic indicates the recorded volts were measured with a 1k/ohms/volt meter. With a DVM the readings will be higher because the DVM does not load the circuit.
Soldered and mechanically made connections to either chassis or other electrical parts with hardware are suspect as after 90 years the metals, including solder are subject to inter-granular corrosion. They may measure O.K. with a DC meter but at RF act like a semiconductor junction. Chassis riveted and solder tabs are suspect.
Your series of Philco used solenoid wound coils with forms that use a celluloid insulator between primary and secondary layers of windings. Over time the celluloid decomposes forming nitric acid, that eats past the enamel and corrodes the windings. A winding must have the resistance given measured with a analog ohmmeter. If it is higher it is corroding, if it is open that is a factor in the putt-putt noises but also lack of signal..
To be true, a DVM is NOT your friend servicing an old radio. After these preliminarily checks on coils, all of them. Remedy what is wrong as well as chassis grounding connections. Then, a stage by stage fault check can resume..
Note large grounding connections to chassis can be more easily re-soldered when the chassis is warmed to 140f with a heat gun and a soldering iron with a large copper mass. Raising up the temp of the soldering iron only burns the flux and accelerates oxidation.
GL
Chas
Soldered and mechanically made connections to either chassis or other electrical parts with hardware are suspect as after 90 years the metals, including solder are subject to inter-granular corrosion. They may measure O.K. with a DC meter but at RF act like a semiconductor junction. Chassis riveted and solder tabs are suspect.
Your series of Philco used solenoid wound coils with forms that use a celluloid insulator between primary and secondary layers of windings. Over time the celluloid decomposes forming nitric acid, that eats past the enamel and corrodes the windings. A winding must have the resistance given measured with a analog ohmmeter. If it is higher it is corroding, if it is open that is a factor in the putt-putt noises but also lack of signal..
To be true, a DVM is NOT your friend servicing an old radio. After these preliminarily checks on coils, all of them. Remedy what is wrong as well as chassis grounding connections. Then, a stage by stage fault check can resume..
Note large grounding connections to chassis can be more easily re-soldered when the chassis is warmed to 140f with a heat gun and a soldering iron with a large copper mass. Raising up the temp of the soldering iron only burns the flux and accelerates oxidation.
GL
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
