1936 Philco model 84 cathedral - Printable Version
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1936 Philco model 84 cathedral - Guest - 05-13-2010
Hi Y'all, I'm a newbie to this forum! I am repairing/restoring a 1936 cathedral for my uncle, and it comes on but just hums. Is there anything I should know besides replacing the 8uF & 4uF power filter capacitor just to get any stations?
Do the RF coils need to be pulled and/or checked before I can receive any stations? It had a bad 77 tube (burned out heater) which is on order.
Re: 1936 Philco model 84 cathedral - vinzer - 05-13-2010
All the caps in the bakelite blocks should be replaced and all resistor values checked and if off value changed ground on 77 tube checked.
vinzer
Re: 1936 Philco model 84 cathedral - hotrod - 05-13-2010
I recommend replacing all the wax/paper capacitors as well.
Rod
Re: 1936 Philco model 84 cathedral - Radioroslyn - 05-13-2010
Lets not forget the feedback winding on the oscillator coil.
At least check it for continuity.
Terry
Re: 1936 Philco model 84 cathedral - Guest - 05-14-2010
Awsome, awsome, awsome! Thank you all very much! Very good info. I was wondering if there were something inside those bakelite blocks. I just now acquired a schematic for this puppy and it shows those paper caps, but could not see them under the chassis! 8)
I was just checking the first coil which I believe (according to the schematic) is the antenna coil. It has good continuity. Which one is the oscillator coil?
Re: 1936 Philco model 84 cathedral - denver - 05-14-2010
You have a # 77 tube with a lead off of it going to the oscillater coil.
Re: 1936 Philco model 84 cathedral - vinzer - 05-14-2010
On my model 84 the osc coil is the center one and mine was open on thr outer winding.
Vinzer
Re: 1936 Philco model 84 cathedral - Radioroslyn - 05-14-2010
Best I remember the winding isn't critical as to the number of turns,about 20 of #30 to 36G should do it and if you wind it in the wrong direction you can just switch the wires that solder to lugs.
Testing
Look at the osc coil and you should see a 6000 ohm resistor and a mica cap (140mmfd) in parallel soldered to one of the lugs. Measure the resistance from that lug to chaiss ground. Should read only a few ohms (3-10) If it is higher pull it a rewind it.
Good Luck w/it
Terry
Re: 1936 Philco model 84 cathedral - Radioroslyn - 05-14-2010
Forgot to mention you said that you measured the antenna coil. Very important that when you check the primary that you have the volume turned up all the way. If you don't then you might be measuring just the volume control not the coil.
Testing
Measure from ant post to ground with volume up and set unplugged. Should be a low resistance like 5-20ohms. If it's up in the 1000's rewind it. The may play with the primary open but it will play much better with it intact. I'd go with 20 or 30 turns of 30-36G wire (not critical).
Terry