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Philco model #20
#5

Hi Rick,

Here is a link to the schematic for the Model 20. It is found in our Philco Library under Documents under early schematics.
https://philcoradio.com/library/index.ph...chematics/


Yes, definitely cut the wire and add a resistor of 970 Ohm +/- 20%. A 1K 5W or preferably 10W resistor will do fine. Having that resistor section shorted raises the voltage across the rest of the divider and puts undue strain on the other resistors in the voltage divider- the subsections of this taped resistor, and definitely the volume pot which is part of the divider. The volume control has 2 sections. One section, connected to points e and F adjust volume by varying the cathode bias. The other section of the volume pot controls the strength of the signal entering the first RF amp. This set has no AVC. Too strong a signal will saturate the 1st and 2nd RF Amp and cut off sound. This is not evidence of an issue with the set.

The filter caps in this set are not electrolytics. they are paper and foil. However, they should be replaced, along with all the other caps. Removing the caps form the can is not very easy, but is doable.

The other caps and some resistors are enclosed in Bakelite "blocks" sealed with tar. Below is a link to an excellent article by Phorum member "Morzh" on how to hollow out the blocks and replace the parts inside without having to desolder the blocks from the set:
https://philcoradio.com/library/index.ph...soldering/

Also attached is a great article on issues with the audio "interstage" transformer, how to "bridge" an interstage transformer with an open primary (a common problem) and how to rewire a good transformer to capacitively couple the primary to the 1st AF stage, removing DC from the primary, extending the life of the transformer and greatly improving fidelity:
https://philcoradio.com/library/index.ph...nsformers/

This is a "TRF" (Tuned Radio Frequency) receiver, which performs rather well. This was a seminal set, as it was introduced in the throes of the Great Depression. This set ushered in the "Cathedral" style, and sold for around $50.00, providing great value for the price.

I am about to crash and burn for the night.

Hope this helps

"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis

Best Regards, 

MrFixr55


Messages In This Thread
Philco model #20 - by onlyrick - 11 hours ago
RE: Philco model #20 - by morzh - 11 hours ago
RE: Philco model #20 - by morzh - 11 hours ago
RE: Philco model #20 - by morzh - 11 hours ago
RE: Philco model #20 - by MrFixr55 - 10 hours ago
RE: Philco model #20 - by onlyrick - 9 hours ago



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