The PHILCO Phorum
Philco 91-121 sensitivity - Printable Version

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RE: Philco 91-121 sensitivity - grandntl - 11-01-2017

If anyone has a 91-121 or 91/221 ( broadcast only) radio and you want to check, please see if your on/off switch has an extra "on" position (far right) that affects the sensitivity. The schematic and 44RF cathode tube socket data don't make sense as shown, thank you Terry, but 25 volts with the switch off and 5 volts with it on could account for this. The schematic and tube voltage data are here: http://www.nostalgiaair.org/Resources/884/M0013884.htm
Bob

RE: Philco 91-121 sensitivity - Ron Ramirez - 11-01-2017

This sounds like either someone adapted the model 15 local-distance circuit to a 91, or else this is yet another of those undocumented factory mods.

Take a look at the model 15 schematic and see if the switching circuit is the same:

http://www.philcoradio.com/images/phorum/schem/15.jpg

RE: Philco 91-121 sensitivity - klondike98 - 11-01-2017

The 91 on my bench at the moment has only the ON-OFF function.

RE: Philco 91-121 sensitivity - grandntl - 11-02-2017

Thank you Ron and Bob, that local/distance switch in the 15 schematic matches what I have. Checking the tube socket data for the 15 shows 30 volts on the 44RF cathode (only one listing). Going back to the 91-121, should all of them normally have 25 volts on the 44RF cathode unless they were a factory or "aftermarket" modification?
Bob

RE: Philco 91-121 sensitivity - grandntl - 11-14-2017

Reading Bob's (klondike98) restoration progress on his 91 and Ron's comments about the on/local/distant switches reminded me of another set of questions. My 91-121 with the three position switch has the remnants of the gold Philco sticker on the chassis that models without the one piece tube shield had (the tube shield has the intact one). Also is there any significance in the stamped numbers on the chassis? I have C49313; there is no visible star like run number. Thank you.
Bob

RE: Philco 91-121 sensitivity - klondike98 - 11-14-2017

I don't believe the C49313 has any useful meaning.