07-15-2019, 11:15 PM
you can test the audio circuit by touching the tip of a soldering iron to the metal cap on the 75 tube. just plug the soldering iron in, don't turn it on. if the audio part of the circuit is working, you'll hear a 60 cycle hum thru the speaker.
you should have about 200 V [DC] at pin 2 of the 78 tube. that's the plate. and the voltage comes thru the IF coil. if you're getting 0 volts, the coil is probably open. but check the voltage coming out of the rectifier [pin 4 of the 84 tube]. it too should be about 200V. and has to be if you're getting sound.
I've found open coils on the RF and IF transformers in similar philco radios out of fords. seems they have a history of corroding. mine had turned green where the wire had corroded away. if you can tune a station that is a multiple of 460 kHz, you likely have a bad IF coil. frequencies 920 and 1380 are harmonic to 460 kHz and generate the IF themselves. see ron's post/thread about the Philco 89 from H**l for other tips. https://philcoradio.com/phorum/showthread.php?tid=6
the IF coils in the ford radios have one coil wound on top of the other. I was able to replace the outer coil which only had 20 or 25 turns as I recall.
you should have about 200 V [DC] at pin 2 of the 78 tube. that's the plate. and the voltage comes thru the IF coil. if you're getting 0 volts, the coil is probably open. but check the voltage coming out of the rectifier [pin 4 of the 84 tube]. it too should be about 200V. and has to be if you're getting sound.
I've found open coils on the RF and IF transformers in similar philco radios out of fords. seems they have a history of corroding. mine had turned green where the wire had corroded away. if you can tune a station that is a multiple of 460 kHz, you likely have a bad IF coil. frequencies 920 and 1380 are harmonic to 460 kHz and generate the IF themselves. see ron's post/thread about the Philco 89 from H**l for other tips. https://philcoradio.com/phorum/showthread.php?tid=6
the IF coils in the ford radios have one coil wound on top of the other. I was able to replace the outer coil which only had 20 or 25 turns as I recall.
