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New to this site and have a Philco 20 question. - Printable Version

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New to this site and have a Philco 20 question. - Guest - 12-01-2006

Hello Philco radio lovers,

I am new to the group and also new to the TRF radio. I wasn't sure if this Model 20 TRF radio functioned normally. I got this radio recently. The radio worked (it received signals). However, the audio garbbled if the radio received strong signals.

It looked like that there wasn't an AGC circuit in the IF and RF sections. I wonder if this was the reason that caused the distorted audio. Also, I wonder if there are mods (such as adding AVC and diode detector) to improve the receiving performance.


Thank you for your answers.

73,

Jonathan,
AB6LS

- Terry Burns - 12-06-2006

Hi Jonathan,
The trf radio has no IF's or avc. Icon_cry It amplifies the rf on the whole band through- out the radio to the detector/first audio amplifier. That is why you get "blaring" on strong signals and have to turn up the volume on weak signals (no avc). Have you recaped the radio yet? A good recapping might be in order. You can find the schematic here. http://www.nostalgiaair.org/PagesByModel/582/M0029582.pdf

Hope this helps
Terry

- Ron Ramirez - 12-06-2006

Jonathan - welcome! Another free schematic may be found here.

For the early Model 20 with only one or two trimmers:
http://www.philcoradio.com/tech/images/20a.jpg

For the common Model 20 with three trimmers on the tuning condenser gang:
http://www.philcoradio.com/tech/images/20b.jpg

The 20 could be modified to add AVC, but it would frankly be more trouble than it would be worth - removing coil ends from ground, adding terminals to coil forms, etc. Not to mention detracting from the originality of the circuit.

- Guest - 12-07-2006

Ron Ramirez Wrote:Jonathan - welcome! Another free schematic may be found here.

For the early Model 20 with only one or two trimmers:
http://www.philcoradio.com/tech/images/20a.jpg

For the common Model 20 with three trimmers on the tuning condenser gang:
http://www.philcoradio.com/tech/images/20b.jpg

The 20 could be modified to add AVC, but it would frankly be more trouble than it would be worth - removing coil ends from ground, adding terminals to coil forms, etc. Not to mention detracting from the originality of the circuit.

Hi Ron and Terry,

Thanks for your feedback. I'd try to see what I can do to make the radio performs a bit better.

I guess the Model 20 probably performs similar to those early 1930 radios or 1920 radio such as Atwater kent Breadboard or Model 20.

Jonathan.