| Don't overlook the mica capacitors. Biased detector and 1st AF amp circuits often have at least one mica cap connected from the plate or B+ circuit to ground. If one shorts, it'll take the plate voltage for that tube to zero. The radio will do exactly what you described -- low hum, no audio. You may also want to check the resistor and mica cap connected from the detector's cathode to ground. If one opens or the cap shorts out, the detector may stop functioning properly. This would also give you no audio, but the hum may be louder. By the way, there are three versions of the Philco 90: One with push-pull 45 output tubes, one with a single-ended 47 output tube, and one with push-pull 47 output tubes. Which one do you have? |
Scott 