Symptums and Solutions: Philco 48-460

[Tubejunke]

I have this radio that I brought back to in what looks to be a very short lived life. Meaning it was a completely dead set and bore an all original compliment of Philco loctal tubes and has a chassis one can eat off of. The on/off switch was all that was wrong with it and I think it could have been a factory defect.

At any rate, I had it playing and it was great. SUPER sensitive to stations across the dial where most radios I have only seem to pull in the stronger stations. After a while I noticed it went silent and I thought to myself there went a cap or whatnot. I turned the tuner and what I got was the whirling radio sounds that remind me more of shortwave than broadcast. The sounds were everywhere there would be a station, yet no station would tune.

I am sure that this is directly connected to a specific section of a AA5 superhetrodyne receiver, but I must admit that exactly which eludes me. Yeah, I could do what I might normally do and willy nilly search under the chassis for something that looks not quite right and most often will be successful. The very unscientific approach is getting old after many years of restoring/repairing old radios. I am more interested in knowing each section )beyond the power supply) and what the outward symptom would be to go along with a failure within that section. I would like to use test equipment that I have to do this at some point. All I have is an oscilloscope, VTVMs' and a signal generator with AF output, but that is the biggest part of what I need.

I'm thinking that perhaps a resistor is changing value over play time and the reason is because I allowed the set to cool and powered it back up and it was normal. One must always consider caps in an unrestored unit as well. Perhaps not as scientific as I hoped, but knowing the section that matches the symptom and starting there would be a more professional approach at radio repair/restoration.