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Philco 90 - someone's been in here before!
#5

I managed to re-wind the coil.  Didn't come out too badly.  I removed the old winding along with the celluloid material, cleaned it with rubbing alcohol, and baked it in the oven at 200 for about 25 minutes.  Then, I used green masking tape as an insulator, and I added roughly 100 turns of AWG 34 copper wire on it, and sprayed it with clear lacquer to protect it.  

   

After reinstalling it in the radio I still had no reception.  I used a little Emerson transistor radio to determine the oscillator was running.  Trying to feed a 175kc signal into the antenna terminal resulted in a barely audible sound from the radio.  I checked the voltages, and figured out that all of the screens in the front end were missing voltages - which they get through a 25k resistor, which, I had connected to the wrong terminal after redoing a bakelite block.  Ugh!  After fixing that, it plays.  

   

A couple things I noticed - it seems very sensitive and selective for an early radio.  Tons of volume, but sound quality is only ok - I'm thinking due to the primitive speaker with a stiff spider.  Also, voltages are all high - probably because of the replacement transformer.  B+ at the rectifier is 310v, so I need to find a way to reduce that.  I also noticed (how I missed this before, I have no idea), all tubes except for the 47 are 6.3v equivalents of the originals, obviously whoever worked on it had trouble finding a transformer with a 2.5v winding.  I don't blame them for converting it over.

I tried to adjust the oscillator at 600kc, and found the adjustment didn't do much.  I might just leave it, it works ok.  I also really need to get grommets for the tuning capacitor, it's completely loose.


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RE: Philco 90 - someone's been in here before! - by adamrobertg - 09-11-2025, 08:22 PM



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