I think this is a home made crystal radio (Wiki) from about
1800 (?)1920s. The "Foote Phila. Pat Pend" is an assembly that has a Geltina crystal in a lead holder, but it has a threaded rod out the back. On the front panel there is a knob that turns a threaded rod with a Berrillium copper spring that can be adjusted so that it touches various spots on the crystal. I was able to adjust it for 2 volts and 0.9 volts (reverse and forward at 1 mA) using a Fluke 87 DMM.
On the upper left corner of the front panel is the ANTENNA connection. The bottom left terminal is GROUND.
On the right lower corner are the PHONES terminals (lower one is ground).
The wire appears to be bailing wire or some other Iron wire, not copper.
The front panel terminals use an 8-32 threaded pinch screw with the threaded portion 5/16" long..
I'm looking for 3 of these.
CircuitFrom ANTENNA to PHONES is the diode.
From ANTENNA to GROUND is a coil, where the upper 10 position switch sets coarse taps and the bottom 10 position switch sets fine taps.
From PHONES hot to PHONES ground is a 20 mmf capacitor that looks like a Copper bar with something wrapped around it and maybe some shim stock sandwiched between two thin wood boards.
This matches the NBS circular 120 design.
Page 12 Receiver
This is probably be the NBS Circular 120 radio.
NBS Circular 120: article about Construction and Operation of a Simple Homemade Radio Receiving Outfit (pdf) - Circular 120 (pdf)
Ref: A Century of Excellence in Measurements, Standards, and Technonogy, David R. Lide, NIST, 2002 - pg 16
stamped in bottom wood in addition
to the name plate s/n.
The FE-50 speaker driver above does not use the lever arm type movement from the Sound Powered Telephones, but it still has great sensitivity.
I got this after studying Sound Powered Telephones and the very efficient speaker elements they used. This speaker driver uses a similar if not the same drive method.
Both of the below patents cover it.
957403 Telephone-receiver, Nathaniel Baldwin, May 10, 1910, 381/418 -
1604251 Telephone receiver, Nathaniel Baldwin, Oct 26, 1926, 381/418; 381/419 -
The Xtal Set Society -
Wiki: Crystal radio
Gollum´s Crystal Receiver World - Crystal Set Testing
Crystal Radio section on Brooke's Electronics web page.
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page created 17 Nov 2001.