Sound Powered Telephone

© Brooke Clarke 2017 - 2019
    Remco Toy Sound Powered Telephone
    Chest Set
    H-203 Handset
    TP-3 Sound Powered Telephone Set
    TA-1 Field Phones
    Baldwin Speaker Driver
        Baldwin Driver + Horn
    Western Electric No. 555 Receiver
    Peerless Speaker (Lektophone)
    Electric Phonograph Pickup Patent 1921
    Murdock Headphones


The Wiki page for Sound Powered Telephones has a number of examples of their use and mentions the USCG regulation that mandates their use on some ships.  The idea is to have an intercommunication system that will work without external power.  This usually is done for reliability rather than cost savings.  The TA-1/PT military field phone is sound powered.  The United States Instrument Corp. set consists of a chest mounted microphone and a pair of headphones.  It as a Jones type connector with 2 male pins.  Not sure of the application.
Dynalec still makes sound powered phones.

In military situations where there is a very high level of background noise, the microphones need to have good noise cancellation properties.  This needs to be combined with the sound powered aspect for a workable sound powered telephone system for military applications.  Note there are no switches which may be in the wrong position in a life threating emergency, i.e. this set is always going to work without any training.

While the telephone that A.G. Bell patented in 1876 used what today we call a dynamic microphone that outputs a voltage (i.e. in a way you could say sound powered) it was replaced in 1889 by the Edison carbon granule microphone that had much higher conversion gain, but required external DC power.

The efficiency of sound powered speakers is much higher than conventional speakers.  Here's the top of page 8 from the Instruction book for the H-203 handset (1938):
Sensivity of Sound Powered Speakers
Notice that the carbon mike has an output that's 25 to 33 dB higher than that of a sound powered mike.

Also, the speaker in sound powered phones is 10 to 20 dB more sensitive than conventional speakers.

In-Ear-Monitor (Wiki)

Balanced Armature (Wiki) headphones/ In-Ear-Monitors are very efficient.  The diaphragm is not stressed like with conventional headphones where a permanent magnet is pulling it.  The professional IEM offer excellent fidelity along with sound isolation.  These are typically custom molded to fit an individual ear & high $$$$$.  Used by professional musicians.
                    Armature Driver
JH Audio: What is a Balanced Armature Driver, Part 2 The Guts and The Glory, The Siren Series: Layla (12 drivers per side)
7194103B In-ear monitor with hybrid diaphragm and armature design, Jerry J. Harvey, Filed: 2005-01-12, Pub: 2007-03-20 - both diaphragm and balanced drivers
8897463 Dual high frequency driver canalphone system, Jerry J. Harvey, JERRY HARVEY AUDIO HOLDING LLC, 2004-11-25 - Laya
8925674 Phase correcting canalphone system and method, Jerry J. Harvey, JERRY HARVEY AUDIO HOLDING LLC, 2015-01-06 - FreqPhase - a similar idea to the Altic Lansing Voice of the Theater speaker where the voice coils of the 15" woofer and the horn driver are in the same vertical plane to prevent sound cancellation/distortion at the 500 Hz crossover frequency.

US20140205131A1 Multi-driver earbud, Apple Inc, 2015-06-09 - in ear uses woofer, midrange and tweeter drivers Some In Ear Monitors (Wiki IEM) use a dozen or more drivers to get high fidelity sound (See JH Audio above)..


The sound from the speaker's voice powers the phone so no external power is needed.


United States Instrument Corp. 1247A G4 Sound Powered Element.  Measures 60 Ohms and makes sound when tested using the Fluke DMM DIODE test function (i.e. 1 mA)

Fig 1 Element sitting in cup (no cover)
                      States Instrument Corp. 1247A G4 Sound Powered
Fig 2 After lifting the element out of the cup.
U.S. Instrument Corp.
U.S. Patent
No. 2224511
                      States Instrument Corp. 1247A G4 Sound Powered
Fig 3
After removing 2 screws to open back cover
                      States Instrument Corp. 1247A G4 Sound Powered
                      Telephone instrument, Turnbull Jr Arthur, Warnke
                      Herbert R, Us Instr Corp, Filed: Dec 4, 1937, Pub:
                      Jun 10, 1941
                      Telephone instrument, Turnbull Jr Arthur, Warnke
                      Herbert R, Us Instr Corp, Filed: Dec 4, 1937, Pub:
                      Jun 10, 1941 2245511 Magnetic sound powered telephone, Berger Samuel I, Oct 26, 1954, 381/418 -

Remco Toy Sound Powered Telephone

This pair of toy sound powered phones was very reasonable on eBay.  The reason is that one of them has a very poor electrical connection and the other about 11 Ohms, but steady.
You can see from Fig 2 below that there's only one sound power element and it serves as both the microphone and speaker.  The problem was they uses a pressure connection between the external terminals and a pair of spring contacts.

After using a pencil eraser to clean the terminals and bending one of the springs out a little the phone halves were mated and the Ohm meter read a solid 11.7 Ohms.  A few drops of acrylic cement (maybe) will complete the repair.

Fig 1
Remco Toy Sound
                      Powered Telephone
Fig 2
                              Toy Sound Powered Telephone
Fig 3
                              Toy Sound Powered Telephone


US2536179 Magnetic sound-powered telephonic unit, Isaac Heller, Remco Ind, Jan 2, 1951, 381/161, 381/418, 381/396   

The bottom two illustrations are of how they make a long bar magnet and break it into small pieces for use in the element.

Chest Set

This set has a strong similarity to the Dynalec UA1814-1 (702020-110) NSN: 5975-01-27, DTID: 3211A0128BH21 but this set has the chest mount microphone support and headphone headbands.

In the movie Submarine: Steel Boats - Iron Men (IMDB)about life on the USS Hyman G. Rickover (Wiki) what appear to be sound powered chest sets are used in many places.

Fig 1 United States Instrument Corp.
United States
                      Instrument Corp. Sound Powered Telephone with
                      chest microphone

H-203/U Handset

This is a handset with Push-To-Talk button.  With the button up the resistance between the 2 leads shows open, when the button is pressed the resistance is about 32 Ohms.   In DMM Diode Test mode when the button is pressed and the leads are brushed against the phone terminals you can hear scratching sounds from both the mike and earphone on the handset.

Switch Plate marked:
Sound Powered Handset Type H-203/U
Stock No. 1N5965-247-0727
Navy Dept. Bu. Ships
Contract No. N001 26-69-G-2303
Serial No. (blank) Insp. (blank)
Receiver Marked:
Alcoa  2
Transmitter Marked:
Alcoa  1

There is a small difference in the elements used for the microphone and speaker, but the fundamental part numbers seem to be the same.

Fig 1 The screw on caps are made of brass, not plastic.
H-203/U Sound
                      Powered Handset
Fig 2
15 MF
200 VDC
H-203/U Sound
                      Powered Handset

Alcoa 2
U.S. Patent
No. 2224511

Alcoa 1
U.S. Patent
No. 2224511


TP-3 Sound Powered Telephone Set

This is a telephone set, meaning that it has ringer capability in addition to the sound powered aspect.  It has the same functionality as the TA-1 Sound powered field phone set below.
This is a derivative of the EE-8 Field Telephone and uses the same outer case (either leather or canvas) and many other parts interchange.  The key difference is that the handset makes use of sound powered elements and so it does not need a battery.  The sound power elements are the same as in the H-203 handset.

There are a couple of blocking capacitors included in this set, one to keep DC out of the sound powered handset and another to keep DC away from the ringer coils/core.  When used with a common battery switchboard an off hook signal to the operator is possible by shorting the L1 and L2 terminals in an alternating pattern of 1 second short 1 second open.


Instruction Book for Telephone TP-3-T1
December 5, 1938
Reprint July 15, 1940

TO 16-40T-P3-5
War Department - 30 August 1944

Technical Data

The handsets measure 36 and 40 Ohms.  About the same as the H-203 above which makes sense since they both use the same elements.

Fig 1
TP-3 Sound Powered
                      Telephone Set
Fig 2 the right side plate is bent.
TP-3 Sound Powered
                      Telephone Set
 From Instruction Book.
This is the same mechanism
as 1767546 Fig 2 (below).
TP-3 Sound Powered
                      Telephone Set
Fig 3
TP-3 Sound Powered
                      Telephone Set

TA-1 Field Phones

Note the ear peice is much thinner on the TA-1 when compared to the The chest set, H-203 or TP-3 above.  That's so that the ear piece can be placed under a helmet.

Fig 1 with carry case
TA-1 Field Phone
Fig 2
TA-1 Field Phone

Sound powered field phones with generator driven buzzer, so no batteries or external power needed.  On separate web pages TA-1.
Earphone element: SM-D-189373
Microphone element: TA-Z21/PT

Baldwin Speaker Driver

The 957403 patent dated May 10, 1910 appears to the the oldest on this web page and is for an efficient sound powered microphone or earphone, but it's not a loud speaker, i.e. there's no large cone.  For that  See the Lektophone.

This earphone driver uses the efficient drive mechanism where the coil axis is at right angles to the disk center axis.
Markings shown in Fig 1:

Nathaniel Baldwin Incorporated
Salt Lake, Utah
Pat. May 10, 1910 - Oct 26, 1926
Nos. 957403 - 1604251

When I used a magnetic polarity tester to determine the polarity of the horseshoe magnet the tester did not respond, meaning that the magnet had lost it's charge.  To recharge it I used a stack of neodymium disk magnets to recharge the horseshoe magnet. (see: K&J Magnetics)

Both of the below patents show some support for the armature on the end opposite the diaphragm drive rod.  The newer patent also shows the pole pieces that look very similar to the photos, but the spring support on the end of the armature opposite the drive rod is missing from this example.
The end of the armature can be moved so is somehow floating.

I attempted to add modern 1/16" thick magnets to the poles of the existing horseshoe and pole pieces, but it didn't seem to offer much improvement over just using a modern magnet to recharge the horseshoe magnet.  Fig 3 & Fig 4 were marked with measurements to help selecting magnets.

                      Telephone-receiver, Nathaniel Baldwin, May 10,
                      1910, 381/418
957403 Telephone-receiver, Nathaniel Baldwin, May 10, 1910, 381/418 -

                      Telephone-receiver, Nathaniel Baldwin, Sep 14,
1153593 Telephone-receiver, Nathaniel Baldwin, Sep 14, 1915, 381/418   
                      Telephone receiver, Nathaniel Baldwin, Oct 26,
                      1926, 381/418, 381/419 1604251 Telephone receiver, Nathaniel Baldwin, Oct 26, 1926, 381/418, 381/419 -

3: horseshoe magent
4 & 5:
pole pieces
9: flat plate armature
Fig 1
                      Speaker Driver
Fig 2
                      Speaker Driver
Fig 3
                      Speaker Driver
Fig 4
                      Speaker Driver

Baldwin Driver + Horn

This is a three part horn. 
The cast iron base holds the driver.
The cast iron neck connects the base to the big horn.
The big horn is made of Bakalite with a sheet metal ring for the connection to the neck

Fig 1
                      Driver + Horn
Fig 2 Note bottom plate of base is friction fit with felt trapped between the two.
                      Driver + Horn
Fig 3 Using the DMM Diode test function produces a loud scratching noise.
Fig 4 Nathaniel Baldwin Incorporated
Salt Lake City, Utah
May 10, 1910   Sept 14 1915
Those are different than the patents listed on the driver above.
They are 957403 and 1153593
Fig 5
Fig 6 "Standard Loud Speaker"

Western Electric No. 555 Receiver

This was the first loudspeaker to be used for talking movies (Wiki).  It consisted of the WE No. 555 moving coil driver coupled with a huge horn to make enough sound for to fill a movie theater.

1707544 Electrodynamic device, Albert L Thuras, Western Electric, Filed: 1926-08-04, Pub: 1929-04-02 - Dynamic moving coil speaker driver - WE No. 555
1729806 Electrodynamic device, Albert L Thuras, Western Electric, Filed:1928-04-26, Pub: 1929-10-01 - increase the efiiciency of electrodynamic devices
1812389 Acoustic device, Edward C Wente, Western Electric, Filed: 1925-04-01, Pub: 1931-06-30 - probably the No. 555 driver "Receiver"

Peerless Speaker (Lektophone)

This speaker was made under the Lektophone Patents as were many early speakers while the patents were in force. 

The label spells this out.

Licensed Under
Lektophone Patents
No. 1271527 - No. 1271529
No. 1271528 - Other Patents Pend.
Manufactured by United Radio Corp. Rochester, N.Y. U.S.A.

This speaker was purchased and it's located on the Sound Powered Telephone web page because the central axis of the coil is a right angles to the central axis of the speaker cone, i.e. an efficient structure.

The speaker measures 1.34 k Ohms.  There is a low pass filter made up of two capacitors and an iron core inductor between the input wires and the speaker proper.  When you look into the front with a flashlight you can see a second cone.  That's to say there are two speaker cones with different cone angles.


Fig 1 Front
                      Speaker Mfg. by United Radio Corp. under
                      Lektophone Patents
Fig 2 Back
                      Speaker Mfg. by United Radio Corp. under
                      Lektophone Patents
Fig 3 Bottom
                      Speaker Mfg. by United Radio Corp. under
                      Lektophone Patents
Fig 4
                      Speaker Mfg. by United Radio Corp. under
                      Lektophone Patents
Fig 5
                      Speaker Mfg. by United Radio Corp. under
                      Lektophone Patents
Fig 6 Coil at top of horseshoe magnet
has it's axis up and down.
                      Speaker Mfg. by United Radio Corp. under
                      Lektophone Patents


---------------------------- Listed on Label ----------------------
Sound-regenerating machine, Marcus C Hopkins, Lektophone Corp, Jul 2, 1918, 369/80, 369/158 - This is a flat record player (not Edison cylinder, Wiki) and instead of using a horn speaker (Wiki)  it uses a large diameter cone that has a rod driving the center point. 
Sound-regenerating machine, Marcus C Hopkins, Lektophone Corp, Jul 2, 1918, 369/158, 369/170 - very similar to the ...527 patent.
Acoustic device, Marcus C Hopkins, Lektophone Corp, Jul 2, 1918, 181/164, 181/173, 181/171, 369/155, 381/432  

-------------------------- Other Patents Pend. ----------------------

1389632 Acoustic diaphragm, Davis William H, Joss Fredrick E, Lektophone Corp, Sep 6, 1921, 181/171 - Just the cone part of a speaker
1829355 Acoustic diaphragm, Houghton Vernon T, Lektophone Corp, Oct 27, 1931, 181/173 about folding the cone outer diameter surface to add compliance.  Modern speaker cones have "ripples" to to that. 

1855168 Loud speaker, Farrand Clair L, Lektophone Corp, Apr 19, 1932, 381/418, 381/432, 181/172 - can be used as either Microphone or speaker.  "'The principal object of this invention is to provide a loudspeaker of the above described general type in which the flexible support for the diaphragm is supplemented by a special flexible support for the armature, which will permit the armature to move freely in an axial direction but will hold the armature, or assist the flexible support for the cone in holding it, in the proper aligned position in the air gap. "  Coil axis is concentric with cone axis so not the high efficiency Sound Powered Telephone design.

Lektophone Corporation v. The Rola Company, 282 U.S. 168 (1930) (Supreme.justia, FindLaw)
"The contribution of Hopkins, if he made one, as held in several cases in the lower courts and abroad, was to combine abandoning the sound box, determining the size of the cone deemed by him most suitable to reproduce the sounds communicated to it by vibration, and tightly gripping and rigidly supporting the outer edge of the above-mentioned annular rim of the cone between two rings. A result claimed for the rigid support, although seemingly not thought of at the time, is to avoid interfering sounds, "blasting" and ratting, that were made when the edge of  the cone was loose."

Lektophone Corp. v. Western Electric Co., 20 F.2d 150, 154 July 12, 1927 - (LEagle)

"There is not to be found in the prior art a sounding board such as Hopkins designed and had patented as his invention, and it is not enough to defeat his patent to say that the elements of his claims are already found in the prior art in isolation or in other combinations."
963362 Apparatus for recording or reproducing sounds, Thomas A Edison, Jul 5, 1910, 369/165; 181/162; 181/173; 369/168 -flat pleated disk, not a cone
986477 Acoustical instrument, Louis Lumiere, Mar 14, 1911, 29/896.23; 369/160 - pleated cone

Lektophone Corp. v. Crosley Radio Corporation, 46 F.2d 126; (CaseText)

Lektophone Corp. v. .S. G. Brown, Ltd. (Wiki), Ch.Div., January 23, 1929 (academic)


Electric Phonograph Pickup Patent

Prior to the early 1920s all the reproducers were mechanical in nature because vacuum tubes (Wiki) were not yet available.

1384295 Electric reproducer for phonographs, Pierre Frely Henry Armagnat An (Paris, France), Jul 12, 1921, 369/148 - prior to this all pickups and reproducers were mechanical.
1531252 Electrical reproducer for phonograph records, Thomas Jones Edward, Wired Radio Inc, Mar 24, 1925, 369/147 - electrical pickup, 2 tube amp, driver & Horn.  Spring motor for phonograph disk.
1536116 Sound reproducer, Martin William H, American Telephone & Telegraph, May 5, 1925, 381/184, 381/432 -  Fig 2 efficient design driving diaphram attached to cone.
1596045 Sound reproducer, Frank J Kaehni, William L Kaehni, Cleveland Trust Co, Aug 17, 1926, 369/9, 123/73.00V - driver moves flat diaphram attached to dish shaped cone, i.e. driving the wrong part.
1734271 Conical-diaphragm sound reproducer, Peterson Charles W, Nov 5, 1929, 181/166 -

Exponential Folded Horn

2338262 Acoustic horn, Vincent Salmon, Jensen Radio Mfg Company, Jan 4, 1944, 181/192, 181/194 cited by 4176731 Altec Corp. dual exponential horn. See Voice of the Theater)

All of the below patents use the same type of element where a rod couples the diaphram to the permanent magnet device.

                      Sound-reproducing device, Mueller Herman C, Jun
                      24, 1930

1767546 Sound-reproducing device, Mueller Herman C, Jun 24, 1930, 381/418, 381/419 - this is a loudspeaker consisting of an exponential horn connected to a removable "driver".  The driver contains a horseshoe magnet. 

This is very similar in function to the
Freed-Eismann Radio Speaker FE-50 and the Baldwin + Horn above.  These speakers needed to be very efficient since they were powered from crystal radios with very low output power.  Note that a speaker of this type can also be used as a microphone.

This patent is cited as prior art by the Roanwell patent 3454912 below.
1886031 Mechanical construction of loud speakers, Langley Ralph HCrosley Radio Corp, Nov 1, 1932, 335/231, 335/281, 335/266, 335/270 -   
2267808 Electromagnetic device, Nelson Blount, Bell Telephone Labor Inc, Dec 30, 1941, 335/231, 381/354 - ..improve the efficiency and operating characteristics.... 

                      Transducer, Howell Arthur S, Stromberg Carlson Co,
                      Dec 25, 1945

2391627 Transducer, Howell Arthur S, Stromberg Carlson Co, Dec 25, 1945, 381/418 - "A telephone of this type is adapted to serve either as a transmitter or receiver thus when two of such, telephones have their respective terminals connected by suitable conductors in an electrical circuit, the arrangement comprises a complete telephone system which operates without an external source of current or power other than the sound from the speakers voice. Such a soundpowered telephone is especially useful for military purposes and therefore it must be small in size so that it can be used in conjunction with a helmet and its construction must be such that it will not bedamaged when overloaded by loud blasts."

Sound translating device arranged to eliminate extraneous sound, Kettler Alfred H, Rca Corp, Filed: Oct 30, 1948, Pub: Jul 15, 1952, 381/372, 381/359, 181/129, D14/249 - a noise cancelling headsest.  Needed because headphones act as microphones when not on a head.  They add noise into a multistation sound powered phone system.  Switches are not good in a emergency situation. 
2611035 Noise-canceling microphone, Duncan Robert K, Rca Corp, Sep 16, 1952, 381/94.9, 381/170, 381/115, 381/91, 381/94.7 - two microphones back to back "noise-cancelling close-talking"
Headset receiver, Kettler Alfred H, Touger Martin L, Secretary of the Air Force, Filed: Feb 27, 1951, Pub: Jul 26, 1955, 381/345, 381/371 - designed to work from sea level to 40,000 feet. 
2896026 Sound
                      powered phone, Kettler Alfred H, Secretary of the
                      Navy, Filed: Nov 2, 1953
2896026 Sound powered phone, Kettler Alfred H, Secretary of the Navy, Filed: Nov 2, 1953, Pub: Jul 21, 1959, 381/177, 381/337, 381/355 - This is about adding an effective noise cancelling capability to a sound powered phone for use on ships during wartime conditions.

2912523 Electro-acoustic transducer, Knowles Hugh S, Mullen Joseph EIndustrial Research Products Inc, Nov 10, 1959, 381/418, 335/301, 335/231, 335/252, 335/235, 310/25, 335/236 - for use in hearing aids as both mike and speaker.  Not susceptible to or cause external magnetic fields so the mike can be close to the speaker.  
3111563 Electro-mechanical transducer, Elmer V Carlson, Industrial Research Products Inc, Nov 19, 1963, 381/418, 335/231 - external magnetic flux changes have no effect on output, i.e. shielded.
3454912 Transducer drive rod, Morrison Louis A, Roanwell Corp, Jul 8, 1969, 335/231, 381/412, 381/396 - headband holds two receivers, adjustable height of each receiver

Murdock Headphones

These may not belong on the sound powered telephone web page, but I've found some patents and his is where I'm parking them.
 655726 Telephone-receiver, William J Murdock, 1900-08-14 - long pole or headphone style
 786588 Telephone-receiver, William J Murdock, 1905-04-04 - long pole
 801034 Telephone-receiver, William J Murdock, 1905-10-03 - long pole
 853186 Telephone, William J Murdock, 1907-05-07 - long pole case molded with woven core
1091528 Circuit-detector, William J Murdock, 1914-03-31 - headset with series battery and test probes = audible continuity tester
1513924 Telephone head set, William J Murdock, 1924-11-04 - similar to 1583088 except pinch screw height adjustment
1583088 Telephone head set, William J Murdock, 1926-05-04 - headband & two earphones, spring clip earphone height adjustment

Brandes Inc

1447969 Telephone head set, Dietrich Frederick, Brandes Inc, 1923-03-13, 379/430; 296/139 - adjustable headband, see YouTube
1536482 Telephone receiver, Dietrich Frederick, Brandes Inc, 1925-05-05, 381/412 - matches design in YouTube video. - specifically mentions ability to take apart without breaking leads, but in video all the leads were broken.
1543325 Headband for telephone head sets,
Dietrich Frederick, Brandes Inc, 1925-06-23, 2/209.3; 381/376 - to fit head of wearer
1544136 Electrical connection for telephone headsets,
Dietrich Frederick, Brandes Inc, 1925-06-30,  381/379; 174/36; 381/189; 381/377 - not exposed terminals so B+ from tube radio will not cause electrical shock.
1645231 Electromagnetic sound reproducer, 
Dietrich Frederick, Brandes Inc, 1927-10-11, 381/160; 381/432 - triangular speaker enclosure
D71138 Loud Speaker,
Dietrich Frederick, Brandes Inc, Sep 28, 1926, D14/211 -

Patents by Henry C Harrison  


Audio - military audio connectors
Aviation Headsets -
Bell System 302 Dial Phone - the "I Love Lucy" phone, this is the first phone I can remember.  The first phone to have all the parts in one case.
Bell System 500 Dial Phone - basis for the REN Ring Equivalence Number that's on the label of all modern phones
Bell system 2500 Touch Tone phone -
Beltone 12D Audiometer
CA-67 Interface Unit, Automatic Data Processing  Stardynamic  5895-01-443-5081
Cell Phones
EE-8 Telephone Set
E-89-A Telephone Repeater
EM200 EM200 Ear Mike
GR650A General Radio GR 650-A & GR 1650B Impedance Bridges
GRsound General Radio Sound Measurement Instruments
GRA-39 Radio Set Remote over phone wire
H161 H-161E/U Headset used in Crew Served Vehicles (2 connectors)
H-207A/VRC Handset
H250 H-250/U Handset with Noise Canceling mike
H251 H-251A/U Headset (earphones)
H33 H-33F/PT Handset
H350 H-350/U Handset
Harris RF-5980-SA001 Amplified Speaker
Harris TS1000 ADSL Test Set -
Harris TSP-21 Telephone Test Set Plus (like but set, but belt-clip & operators headset
Home Theater - 7.1 Surround Sound - Voice Of The Theater Speakers (very efficient)
HP204 HP 204B Audio Oscillator from HP 3350 Carrier Test Set (AN/USM-181 Telephone Test Set
HP241A HP 241A Audio Oscillator w/Radio Buttons
HP415E HP 415E SWR Meter - 1 kHz tuned voltmeter
HP4260 HP 4260A Universal Bridge
HP 4261A LCR Meter
HP427A HP 427A Voltmeter AC & DC Volts & Ohms
HP4274_4275_LCR lHP 4274A & HP 4275A LCR Meters
HP4332 HP 4332 LCR Meter
HP 4395A HP 4395A Combination Network, Spectrum, Impedance Analyzer includes audio frequencies
HP33120 15 MHz Function/Arbitrary Waveform Generator
HS2B4 Plantronics Supra  -01NC 992C Headset
HS30A HS-30-A Headphones, CD-604 Transformer
HYX-65-1 Wire-line Adapter Local Unit & KY-65
KS-8455L2 Kick Test Set Line Loop Tester Telephone Installers & Repairman's Meter
KY68 KY-68 Secure Field Telephone
LS-147 Intercom
LS454 LS-454/U Loudspeaker
LS-685/U Crystal Loudspeaker
LS-688 PM Loudspeaker
M1024 Magnacord 1024 Reel to Reel Tape Recorder
M153 M-153/U Microphone, Voice Silencer
M80 M-80/U Handset (Microphone)
MAA Military Audio Accessories - tables with thumbnail photos & links to more info.
MATEL 2C800 Field Phone by Racal Acoustics Ltd.
MK-356/G Wire Splicing Kit
MRC67 MRC-67A Amplifier-Speaker
No6 - No. 6 Dry Cell
Noisecom 7110-FAC Programmable Noise Generator
NSLB Model NS-LB Noise Generator
Panasonic KX-TA824 Telephone System
PatchP Audio Patch Panel
Racal MATEL 2C800 Field Phone
RS 38-A Carbon Microphone
RT1185 RT-1185/GRA-114 Sound Observer Receiver Transmitter
SB-22A Analog  Switchboard
SB-4170 Digital Switchboard
SB-3614A(V)/TT Telephone Switchboard
SG-886A/UR Interference (Noise & Tone) Generator
SidekickTandN Tempo Sidekick T&N Telephone Line Tester
Spying on Cell (Mobil) Phones
Subscriber Loop Analyzers
TA-1 Sound Powered Telephone Set
TA-1042  Digital Non-Secure Voice Terminal (DNVT)
TA-312/PT Telephone Set  (Field Phone)
TA-838/TT Telephone Set
Teledyne Avionics TA-3D Acoustic Impedance Meter - ear canal impedance
Telegraph Telegraph Equipment, Stock Ticker, District Telegraph, Teletype, Keys, Relays, Sounders, Veedre Counter, Early Connectors, Electro-magnets
Telephone Patents & photos
Telephone Tool Kit
Telephone Poles - Utility, Power, Cable TV Poles
Tempo Sidekick T&N Line Tester
TF2700 Marconi TF-2700 Universal Bridge
TG-5-B Telegraph Set
Tone & Probe station wire testing
TS-2839/GY German H-33 Audio Test Set
TS-3647/G, Control Orderwire Unit (COU), Telephone Test Set
TS585 TS-585 Audio Level Meter
TSD-3600 Telephone Security Device
TSEC/KY-68 Digital Subscriber Voice Terminal
U229AA U-229 Audio Accessories
U229PO U-229 Pin Out by Function
U229Y "Y" Cable,  U-229/U
UIQ10 UIQ-10 Public Address Set
VIC VIC Vehicle Inter Communication & VRC-12 Series Radios
Voice Over Internet Protocol (VOIP) Phone Service
Western Electric 202 Dial phone- consists of a phone and a "sub set" that's mounted on the wall.
WE 500 Dial Phone -
Western Electric 2554 Wall Touch Tone Telephone
WTFME1 Funkanpaßgerät WT-FM-E1 AP01 Telefunken Military wire to radio interface
Xtal1800 Crystal Radio 1800? & Brooke Clarke #1 & horn speaker
ZM-4B/U Resistance Bridge
Zo Transmission Line Zo vs. Frequency - down to audio



PRC68, Alphanumeric Index of Web pages, Contact, Products for Sale
Page Created  2017 October 13