NBS Circular 120 Crystal Radio & Brooke Clarke #1

©Brooke Clarke, N6GCE 2001 - 2023

1800s Crystal Radio Description
     NBS Circular 120
A Crystal Radio by Brooke Clarke
Freed-Eismann Radio Speaker FE-50
Baldwin Speaker Driver
Heathkit CR-1
Dummy Antenna & Load
                      Circular 120 Crystal Radio
                      Circular 120 Crystal Radio
                      Crystal Radio
                      Crystal Radio
Foote Phila.
Pat Pend
adjustable Crystal assembly
20 mmf Capacitor

1800s Crystal Radio Description

June 2022: UPDATE:  This is the NBS Circular 120 Radio.

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.

NBS Circular 120

From 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.
Crystal Radio
                  NBS Circular 120
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

Galena Holder

879117 Rectifier and Detector, G.W. Pierce, Massachusetts Wireless Equipment, 1908-02-11, 257/613 257/41 252/62.3V 329/370 -
1122358 Detector, Lester Stewart Barr, 1914-12-29, 257/41 -
1104065 Detector for Wireless Apparatus, B.J. Miessner, 1914-07-21, 257/41 -
1104073 Detector for Wirlelss Telegraphy and Telephony, G.W. Pickard, Wireless Specialty Apparatus, 1914-07-21
RE13798 Means for Receiving Intelligence Communicated by Electric Waves, G.W. Pickard, 1914-09-08, 329/347 439/8 257/41 403/24 -
1290755 Wireless Detector, S.S. Jones, 1919-01-07,
257/41 439/8 -
1496671 Detector, H. Gernsback, 1924-06-03,
257/41 252/62.3R -
1515994 Oscillation Detector, A.W. Bowman, 1924-11-18,
257/41 -
1576783 Radiodetector, J.B. Pitts, 1926-03-16,
257/41 -

Patents in class 257/41 - published after W.W.II relate to the 1N21 microwave point contact diode.


In the same lot as this radio there were two pair of headphones.
Federal Telephone and Telegraph Co., Buffalo, N.Y., U.S.A. Type 53-W, 2200 Ohms.
The other pair is marked with a "M" on the center of the back and the number 1000 is stamped on the coil inside.

A Crystal Radio by Brooke Clarke

This radio was made in the late 1960s or early 1970s.  This was during a time when I was spending a lot of time with the Boonton 160 Q meter and making a number of coils. 
The cardboard box has suffered from both the time and having stuff on top crush it.
Brooke Clarke
                Crystal Radio #1
Brooke Clarke
                Crystal Radio #1
Brooke Clarke
                Crystal Radio #1
The antenna circuit consists of the range switch on the left, the tapped coil (horizontal over red earphone binding posts) and the two section air variable cap on the left.  A clip lead not in the photo is used to connect to one of the taps.  The idea is to resonate the external antenna.  The antenna and ground (must have a good ground) are connected on the back.  The antenna circuit has a coil that couples to the tank circuit, but there's no metallic connection between the antenna circuit and the tank circuit.  The tank is composed of the three section air variable cap and the other part of the standing coil.  Uses a 1N34 diode and hi impedance (old) headphones.

With a 100 foot long wire this receiver picked up all the AM broadcast stations you would hear on a regular table radio.  The best way to tune is first set the tank where the station will be then peak the antenna circuit.  There's a small amount of interaction between the antenna circuit and the tank, but not a lot.

KGO, which  is the San Francisco 50 kW clear channel station, would drive a loudspeaker so ear phones were not needed.

Freed-Eismann Radio Speaker FE-50

This speaker came with what I think is a nice Neutrodyne radio and a few battery eliminators.  It's composed of a driver and an exponential horn.  The driver is made by Dictograph (patent 1668509).  It weighs about 15 ounces, you definitely would NOT use a pair of these for earphones, way too heavy.  But that may be part of why it works so well.  When used with the above crystal radio it provides enough volume from a strong station to hear on the opposite side of the room.   Probably made under patents (see below): 1563500, 1621845 & 1668509 so probably made 1928 or later.  The label on the back of the box reads:

The Freed-Eismann Radio Speaker FR-50
caption under photo of speaker sitting on top of radio:
"The NR-6 and the FE-50 Radio Speaker.
This Radio Speaker is equipped with a reproducing unit which does not require any adjustment at all.  Do not under any circumstances tamper with the unit.  The Radio Speaker should preferably be placed directly on top of your receiver as shown in the accompanying figure.  In connecting up this Radio Speaker for the first time, it is important ot get the polarity of this Radio Speaker correct.  Try the Radio Speaker with it's leads connected to the telephone plug (or the receiver binding posts) in one way, then disconnect and reverse the Radio Speaker leads.  In one of these positions the signal may be clearer and louder than in the other.  Leave the Radio Speaker permanently connected with the connetions giving best results.  In the event you should ever obtain a persistent howl, it may be due to:
1- A defective detector tube.
2- Run down B Batteries.
3- Acoustic resonance.
  Occasionally, if a Radio Speaker is placed in a small room or in a room in which the reflection of sound is very great, a sustained howling may be produced, and this may be overcome by separating the Radio Speaker from the receiver by putting a small piece of cardboard under the Radio Speaker to raise it from contact with the top cover of the cabinet, or it may be necessary to remove the Radio Speaker from the top of the set and put it on a table alongside the set.  The guarantee on this Speaker does not hold if serial number of bottom of cabinet is in any way defaced."
FE50FreqResp.avi Video of frequency response.  about 200 to 3000.  Can hear 1 kHz with 80 mv input.  DC resistance of input is 4 k Ohms.  P = V*V /R = 0.08 * 0.08 / 4000 = 1.6E-6 watts or 1.6E-3 mW or 28 dB below 1 mw or close to 1 micro W.

An exponential horn (Wiki) is the best way to match free space to the driver.
Freed-Eismann Radio
                Speaker FE-50 Front
Freed-Eismann Radio
                Speaker FE-50 Back
FE-50 Serial Number
331 s/n stamped in bottom wood in addition
to the name plate s/n.
FE-50 s/n Stamped
                in wood in addition to the name plate
Driver Freed-Eismann
                Radio Speaker FE-50
Driver & Horn
                Freed-Eismann Radio Speaker FE-50
Dictograph Radio
                Phono-Unit Front
Dictograph Radio
                Phono-Unit Back

Dictograph Patents

967747 Transmitter Mouthpiece, O.F. Falk (Dictograph), Aug 16, 1910, 381/344 - better shape to transfer more sound energy
1356634 Rheostat for Telephonic Insruments, Henry Koch (Dictograph), Oct 26 1920 - for hearing impaired users
1361590 Telephone Transmitter, Henry Koch (Dictograph), Dec 7, 1920, 379/428.01 ; 191/12.2R; 439/18; 439/30 - passenger to chauffeur
1372437 Telephone Switch Seperator, Henry Koch (Dictograph), Mar 22, 1921, 200/275 ; 200/1TK; 200/237; 379/325 -
stamping insulators for lever switches instead of turning them of screw machines.
1501670 Winding Machine, Henry Koch (Dictograph), Jul 15, 1924, 242/437.4 - Electromagnet Winding Machine
1501694 Signal System for Telephones and the Like, F.H.N. Wohlers (Dictograph), Ku; 15, 1924, 379/171 ; 340/825.41 - Intercom system
1545585 Extensible Cable Unit, Henry Koch (Dictograph), Jul 14, 1925, 191/12.2A
 used for telephone cord boards to retract the cord or for a telephone cord between a wall and the phone
1545627 Cable Support, F.H.N. Wohlers (Dictograph), Jul 14, 1925, 200/61.14 ; 191/12.2A -
 used for telephone cord boards to retract the cord or for a telephone cord between a wall and the phone
1548325 Telephone Receiver, Henry Koch (Dictograph), Sug 2, 1925, 381/417 - strain relief looks like what's used for headphones
1551722 Telephone Signal Device, F.H.N. Wohlers (Dictograph), Sep 1 1925, 379/102.07 ; 200/1TK - Intercom switch and indicator
1551723 Transmitter, F.H.N. Wohlers (Dictograph), Sep 1 1925, 381/180 -
improved carbon ball transmitter where it can survive dropping.  probably for passenger to chauffeur or Dictaphone use.
Reference to 844635
1563500 Loud Speaking Receiver Unit, Henry Koch (Dictograph), Dec 1 1925, 381/433 ; 381/411 -
designed to fit the horn of a phonograph
copending application 628709
Has the appearance of this unit
1579369 Battery Carrier and Connector, Henry Koch (Dictograph), Apr 6, 1926, 429/99 ; 192/110R -
improved battery holder for a couple of "F" (?) dry batteries.  Prior art holders used flexable wrap and filler or could not be reused because the battery had gone dead and swollen up.  Looks like the same batteries as used for the Moxley - Light Weight Railroad Lantern.
1621845 Loud Speaking Telephone Receiver, Henry Koch (Dictograph), Mar 22, 1927, 381/411 ; 381/340; 381/396 -
designed for use with radios where there is voltage and current in addition to the AC audio signal. 
Also includes an extension of the knob to move it outside the speaker box.
shows the beginning of the horn.
looks like this unit, except for the knob extension.
1668509 Sound Reporducing Device, Henry Koch (Dictograph),  May 1, 1928, application s/n 114888, 340/391.1 ; 381/396 -
Looks like this unit
On the back is a "Patents Pending" and on the front is stamped, not cast like all the other markings,  "P33881" which must be a serial number.
1647182 Telephone Receiver, Henry Koch (Dictograph), Nov 1, 1927, 381/411 - air gap between diaphragm and pole pieces.
Application s/n 674601 & co-pending applications 628709 & 661596 all for Loud Speaker improvements
2089402 Battery Holster, S. Murray (Dictograph), Aug 10, 1937 224/624 ; 182/3; 224/902; 224/930-
 for carrying hearing aid battery probably made from shoulder holster for revolver
2405433 Bone Conduction Audiphone, Henry Koch (Dictograph), Aug 6, 1946, 381/151 ; 381/417 -
RE23125 Bone Conduction Hearing Aid, Henry Koch (Dictograph), Jun 21, 1949, 381/151 ; 335/231; 381/162; 381/378; 381/380
uses electromagnets to move plunger that transmits sound directly to the skull.
Dictograph has many many more patents, these were chosen as being in the approximate time frame as the Loud Speaker driver.  They seem to have a number of very innovative patents just in this list.

Baldwin Speaker Driver

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 -    

Heathkit CR-1

Trying to understand dummy antennas to allow testing this radio and the other crystal radios.

Heathkit CR-1
                  Crystal Radio

See: Heathkit CR-1 Crystal Radio and Miller 595 Tuner Information - for details on the CR-1 and an improved version using a toroidal core inductor.  Some information about the Miller crystal set is included (the construction of L1, L2 & L3).
Here's an ad for the J. W. Miller 565.
Some docs on the J.W. Miller Crystal Radio -
eBay: Pirate Pete Electronics - Reproduction CR-1 Kit  - uses plastic tube with a couple of pre-placed ferrite cores & Litz wire to wind the two coils. - he also sells a reproduction Knight Radio Broadcaster kit (I had one of these).  The kit does not have the two 50C5 and one 12AX7 tubes that need to be acquired.

Dummy Antenna & Load

Dummy Antenna

The IRE Dummy antenna can be made using a series 15 Ohm resistor and 20 uH coil between the signal generator and antenna terminal on the radio.
A 10 Ohm resistor between the signal generator ground and radio ground that can be used to measure the input current (for calculating input impedance).

In Wireless Age Oct 1922 pg 68:
400 pf series cap, 25 Ohm series resistor, 28 uH series inductance.

RMA Dummy Ant:
Signal gen hot - parallel circuit [ one leg 20 uH, other leg 400 pf in series with 400 Ohms] then 200 pf in series - radio ant terminal
Signal gen gnd - radio gnd.

Dummy Headphones

2000 Ohm resistor (optionally bypassed with 0.01 uF)


Crystal Radio section on Brooke's Electronics web page.
One Tube Raio - Lee De Forest patent preceeded the Armstrong patent
Sound Powered Phones & Early Loudspeakers


Crystal Radios - general info & Q of coils
Crystal Clear: Volume 1 by Maurice L. Sievers
Crystal Clear: Vintage American Crystal Sets, Crystal Detectors, and Crystals: Volume 2 by Maurice L. Sievers;
crystal-radio.eu -
The Xtal Set Society -
Wiki: Crystal radio
Gollum´s Crystal Receiver World - Crystal Set Testing

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page created 17 Nov 2001.