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Philco 80 missing part - Printable Version

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Philco 80 missing part - llhat - 06-18-2014

Rebuilding a Philco model 80, I used all the advice from Ron Ramirez. I had already rebuilt one of these, so it was easy to remove the second IF transformer to replace the factory 4 megohm with a 2 megohm. Imagine my surprise when I found no 50 mmf in parallel with the resistor which had changed to 6.6 megs. It was easy to put a 50 mmf from my stock but I was amazed that such a radio with a missing part came out of the Philco factory. It must not have been very sensitive. I could tell that no one had removed that coil previously. Interesting mystery.

RE: Philco 80 missing part - Ron Ramirez - 06-18-2014

Later production 80 sets added a turn or two of wire around the IF transformer in place of the 50 pF cap; this loop is open-ended (only one end of the wire is connected).

See: http://www.philcoradio.com/tech/images/80acan.jpg

The 81 and 84 used the same type of IF transformer, also without the 50 pF cap.

RE: Philco 80 missing part - morzh - 06-18-2014

Interesting.

Without this cap the Grid Leak detector should simply not work.
The radio could use some parasitics and still detect, but not via grid leak.
Unless they had some non-obvious cap there.

RE: Philco 80 missing part - morzh - 06-18-2014

Is that phantom winding shown in the sch the cap replacement?

RE: Philco 80 missing part - Ron Ramirez - 06-18-2014

Yes.

RE: Philco 80 missing part - llhat - 06-19-2014

Thanks to all for the response. I knew that the model 84 used the few turns of wire instead of a capacitor. The 84 schematic shows that. There was no such wire in my model 80 IF transformer. Morzh is right the radio did not work well at all without the capacitor. It is much more sensitive now with the grid leak capacitor. I am still amazed that the radio made it past Philco inspection.

RE: Philco 80 missing part - Randy H. - 06-19-2014

More surprising is that it has SURVIVED! You would think that by this time it would have been trashed! Glad it wasn't, and that it fell into the hands of someone who could recognize the 'Factory Error'.

RE: Philco 80 missing part - morzh - 06-19-2014

Indeed. Especially the 80, the "teaser" "under-radio" Icon_smile

RE: Philco 80 missing part - markmokris - 05-05-2015

I am starting some work on a Philco 80. In a 2014 post, this gentleman mentions:

"Rebuilding a Philco model 80, I used all the advice from Ron Ramirez. I had already rebuilt one of these, so it was easy to remove the second IF transformer to replace the factory 4 megohm with a 2 megohm. Imagine my surprise when I found no 50 mmf in parallel with the resistor which had changed to 6.6 megs. It was easy to put a 50 mmf from my stock but I was amazed that such a radio with a missing part came out of the Philco factory. It must not have been very sensitive. I could tell that no one had removed that coil previously. Interesting mystery."

Is there a tech tip or information on this 4 meg to 2 meg replacement? Or the 50mm capacitor replacement? Should I expect to need to make a mod like that?

Thanks,

Mark K8KZ

RE: Philco 80 missing part - Ron Ramirez - 05-05-2015

I wrote this up several years ago and gave it to Chuck to put on his page:
http://www.philcorepairbench.com/tips/svctip44.htm

Only early production 80 sets have the 50 pF cap. Later, Philco changed the IF transformer so that it has a capacity winding instead of the 50 pF cap. If you follow the link in this post and look at the partial schematic there, notice the little curl just above and to the left of the 4 meg resistor (16) - that is the capacity winding which replaced the 50 pF cap.

Yes, your 80 will definitely work better by replacing the 4 meg resistor with a 2 meg resistor.

More 80 mods:
http://www.philcorepairbench.com/tips/svctip43.htm

RE: Philco 80 missing part - markmokris - 05-05-2015

Hey Ron,

Question about the "gimmick" capacitor.

I finished work on a Model 19 cathedral a little while back. I had rewound the tickler coil a number of times trying to get even minimal performance out of that 36 oscillator. My last and most recent rewind seemed to work the best, though that is to say, barely at all. I had done the coil baking and from what I could tell, I followed all the advice available.

However, when I soldered a 2 foot piece of hookup with to the cathode of the 36 tube and just let it poke out the back, the radio comes to life and works beautifully across the entire BC band. I tried various mica capacitors to replace the capacitance I supposedly introduced by the wire (gimmick capacitor?), but no luck.

My next step would have been to do the 6A7 mod, and I still may do that. However, I was suffering from "Model 19-fatigue", so I left the radio as-is for now.

Why have you never recommended the 36 cathode-gimmick capacitor for the Model 19 like you did for the 80 and 84 models?

BTW...I really appreciate all your great advice as well as that of so many other members on Philco Phorum.

Mark K8KZ

RE: Philco 80 missing part - Ron Ramirez - 05-05-2015

Different radio, different design. Apples and oranges.

Model 80 is a regenerative radio; Models 19 and 89 are not.

Model 80 needs all the help it can get just to pick up signals as it was designed as a "price leader" just to get people into the stores where it was the salesman's job to try to sell the customer a more expensive Philco. The ploy backfired with the 80, and nearly 200,000 were sold.

Models 19 and 89, when properly operating, do not need any help to pick up signals as they are much better radios (not regenerative).

Model 80 has no RF amplifier stage; Models 19 and 89 do.

Your 19 should not require any "gimmick" capacitor. That it needs this wire to operate indicates that you 19 still has problems.

Please continue discussion of your 19 in your thread on your model 19 to avoid confusion. Thanks.