NBS Circular 120 Crystal Radio & Brooke Clarke #1
N6GCE 2001 - 2023
adjustable Crystal assembly
20 mmf Capacitor
1800s Crystal Radio Description
June 2022: UPDATE: This is the NBS Circular 120
I think this is a home made crystal radio (Wiki)
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
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
The wire appears to be bailing wire or some other Iron wire,
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.
|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
Rectifier and Detector, G.W.
Wireless Equipment, 1908-02-11, 257/613 257/41 252/62.3V 329/370 -
Stewart Barr, 1914-12-29, 257/41 -
Detector for Wireless Apparatus, B.J.
Miessner, 1914-07-21, 257/41 -
Detector for Wirlelss Telegraphy and Telephony, G.W.
Specialty Apparatus, 1914-07-21
Means for Receiving Intelligence Communicated by Electric Waves,
Pickard, 1914-09-08, 329/347 439/8 257/41 403/24 -
Wireless Detector, S.S.
Jones, 1919-01-07, 257/41 439/8 -
Gernsback, 1924-06-03, 257/41 252/62.3R
Oscillation Detector, A.W.
Bowman, 1924-11-18, 257/41 -
Radiodetector, J.B. Pitts,
1926-03-16, 257/41 -
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
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.
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
The cardboard box has suffered from both the time and having stuff
on top crush it.
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
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."
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.
stamped in bottom wood in addition
to the name plate s/n.
Transmitter Mouthpiece, O.F. Falk (Dictograph), Aug 16, 1910, 381/344
- better shape to transfer more sound energy
Rheostat for Telephonic Insruments, Henry Koch (Dictograph), Oct
26 1920 - for hearing impaired users
Telephone Transmitter, Henry Koch (Dictograph), Dec 7, 1920, 379/428.01
; 191/12.2R; 439/18; 439/30 - passenger to chauffeur
Telephone Switch Seperator, Henry Koch (Dictograph), Mar 22, 1921,
; 200/1TK; 200/237; 379/325 -
stamping insulators for lever
switches instead of turning them of screw machines.
Winding Machine, Henry Koch (Dictograph), Jul 15, 1924, 242/437.4
Signal System for Telephones and the Like, F.H.N. Wohlers
(Dictograph), Ku; 15, 1924, 379/171
; 340/825.41 -
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
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
Telephone Receiver, Henry Koch (Dictograph), Sug 2, 1925, 381/417
- strain relief looks like what's used for headphones
Telephone Signal Device, F.H.N. Wohlers (Dictograph), Sep 1 1925,
; 200/1TK - Intercom switch and indicator
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
Loud Speaking Receiver Unit, Henry Koch (Dictograph), Dec 1 1925,
; 381/411 -
designed to fit the horn of a
copending application 628709
Has the appearance of this unit
Battery Carrier and Connector, Henry Koch (Dictograph), Apr 6,
; 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
Loud Speaking Telephone Receiver, Henry Koch (Dictograph), Mar 22,
; 381/340; 381/396 -
designed for use with radios where
there is voltage and current in addition to the AC audio
Also includes an extension of the knob to move it outside the
shows the beginning of the horn.
looks like this unit, except for the knob extension.
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.
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
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
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
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 -
Trying to understand dummy antennas
to allow testing this radio and the other crystal radios.
Dummy Antenna & Load
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
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
Signal gen gnd - radio gnd.
2000 Ohm resistor (optionally bypassed with 0.01 uF)
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;
The Xtal Set Society
Crystal Receiver World - Crystal
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page created 17 Nov 2001.