Philco 38-3XX chassis repair questions

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Philco 38-3XX chassis repair questions

Post by Rich K. on Sat Nov 30, 2013 10:35 pm

Finally got around to getting the chassis and speaker out of my 38-3XX this evening. After replacing the missing top center dial lamp (the one that makes the illuminated "dial pointer" work), I started looking the rest of the chassis over. It looks like a nightmare to work on, mainly because there is a sub-chassis (RF section?) assembly on top of the main chassis that is attached to the complicated dial mechanism via the tuning capacitor.

My first question is, is there a "best way" to remove the sub-chassis from the main chassis without disassembling EVERYTHING (i.e., the entire tuning dial assembly), so I can replace the paper-and-foil capacitors and anything else that may need replacement under there (rotted wire, bad resistors, etc.)?

My second question is, I want to install a monaural RCA jack and switch into the circuit so I can hook up my 1947 Pilotuner T-601 FM tuner to the radio without making the hookup permanent (I could also use it to plug my phonograph in, too). Where and how do I need to hook up the jack and switch, so that it disconnects the IF (to prevent bleed-over) and allows me to use the audio section for the Pilotuner? Here is a similar set-up that was done on a Silvertone 1970A I used to have, but I had "help from the experts" on that one as well...


Philco 38-3XX schematic HERE

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Re: Philco 38-3XX chassis repair questions

Post by jerryhawthorne on Mon Dec 02, 2013 4:44 pm

Rich, I have worked on a couple of the Philcos with that RF sub chassis and never had the courage to remove it.  I could get to all but one of the wax caps in there.  There are several threads on the Philco Phorum of people doing it, indicating it is not all that bad.  Sure!  As I recall there was a bit of discussion on the procedure.
As for your mono input question, the drawing you posted looks good.  Just go to the "high" side of the volume pot on your Philco (item 68) and lift the wire off.  Extend that wire (shielded cable with the shield grounded) add a second to the lug that one was attached to and route both to where you want your connector/switch.  Should work fine.
Good luck, I hate those sub chassis.
Jerry

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Re: Philco 38-3XX chassis repair questions

Post by Wildcat445 on Mon Dec 02, 2013 7:16 pm

Getting to that one last cap under the sub-chassis is certainly no fun. Probably more fun than trying to get that tuning mechanism working properly again. If you dig and poke and tug, you will eventually get it. There should be some bakelite capacitor assemblies in that radio, too.

Regards

WC

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Re: Philco 38-3XX chassis repair questions

Post by Dr. Radio on Tue Dec 03, 2013 1:27 am

I quick peak at the schematic shows the typical Philco power input, you have a cap from each side of the AC line to the chassis, so you always have the chassis connected to voltage no matter how the plug is inserted in the wall outlet. This can present a hum/shock hazard by connecting the ground side of your audio input to chassis ground. Ideally you'd want to use some sort of isolation such as this set-up
http://www.antiqueradio.org/iPodAdaptor.htm

I don't know what issues running the other-than-an-iPod may make, but due to the safety aspect, I felt it bears bringing up.
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