[rfeenstra]

To change the direction of this thread just a bit, since this is the first "HI-FI" AM radio I've had experience with, I decided to play with the  selectivity control a bit.  I fed the radio a modulated RF signal to the antenna terminal and varied the modulation frequency from 30 Hz to 10K Hz.  With the selectivity control in the fully clockwise position (narrow band width), anything above 5kHz was highly attenuated.  In the counter clockwise position, 8kHz was attenuated but still significant on the scope connected to the voice coil.  My ears are getting old, I know, but I couldn't hear much above 7.5kHz.  I don't think the speaker is capable of it.  I kind of wish Philco had separated the Treble control from the selectivity control.  It would have given better control over the intensity of the high frequencies.

For fun, I did the same thing with my Scott 16A from 1947.  It's speaker is a coaxial and has a little better high frequency response.  Interestingly, even a 10kHz signal is significant on the scope, yet selectivity is good.  I can hear the the sign wave to above 8kHz., which is probably where my ears drop off.  Evidently, they learned how to give a wide AM frequency response and still maintain a degree of selectivity.  Perhaps this is why the "HI-FI" AM sets kind of disappeared after '38, '39????  Or was it the prospect of FM coming soon?

I am enjoying playing with this radio as it sounds good and is quite sensitive.  The automatic tuning and Magnetic tuning work well.  Bass response is excellent and well balanced.  Perhaps the passive radiators (acoustic clarifiers) have something to do with that.  This has been a fun experience and all of your input and comments have been a great part of it.  Thank you!!!