02-28-2021, 06:54 PM
Thank you for the replies. I will be experimenting with the external audio connection this coming week.
I managed to repair the magnetic tuning today. I took apart the original can again to look at the coil. I had replaced the 110PF cap and the 490K resistors already and the primary was causing the required dip in audio. I tried replacing the 80PF mica that was in parallel with the secondary trimmer, thinking maybe it was bad. No dice. I could not get enough capacitance and the trimmer was down tight. I tried experimenting with extra fixed mica caps and still no change.
I decided to remove the transformer from the parts chassis. When I opened it to change the resistors, it was built completely different. The secondary had a big ole air variable cap and no fixed mica across it. The primary was identical to the old one. This transformer reminded me of the one in the 38-690.
After changing the resistors and installing it, the magnetic tuning worked perfectly! I had to tweak everything slightly, but that's it. Something must have been wrong with the coil in the old one. Philco must have had issues in the original design and went to this model. Hopefully this info will help someone working on one of these models.
I managed to repair the magnetic tuning today. I took apart the original can again to look at the coil. I had replaced the 110PF cap and the 490K resistors already and the primary was causing the required dip in audio. I tried replacing the 80PF mica that was in parallel with the secondary trimmer, thinking maybe it was bad. No dice. I could not get enough capacitance and the trimmer was down tight. I tried experimenting with extra fixed mica caps and still no change.
I decided to remove the transformer from the parts chassis. When I opened it to change the resistors, it was built completely different. The secondary had a big ole air variable cap and no fixed mica across it. The primary was identical to the old one. This transformer reminded me of the one in the 38-690.
After changing the resistors and installing it, the magnetic tuning worked perfectly! I had to tweak everything slightly, but that's it. Something must have been wrong with the coil in the old one. Philco must have had issues in the original design and went to this model. Hopefully this info will help someone working on one of these models.
Tony
“People may not remember how fast you did a job, but they will remember how well you did it”
