Radio Boulevard
Western Historic Radio Museum
 

Vintage Microphones


Radio Broadcast Microphones

RCA, Western Electric
 

General Purpose Microphones

Shure Bros. Inc., Electro-Voice, Astatic Microphone Laboratory, Inc.,
The Turner Co., American Microphone Co., Other Mfgrs.
 

Carbon Microphones

Military, Shure Bros., Kellogg, Universal Microphone Co.

Astatic Microphone Laboratory, Inc.

The Astatic D-104 crystal microphone was introduced in 1933. It became the quintessential "ham" mike due to its high output, its high impedance and its great upper frequency audio response. Astatic regularly held photo contests in the thirties (up to about WWII) for the best photograph that they thought represented the ham operator and Astatic. This $100 award winner was used on the 1937 Astatic Microphone Laboratory brochure.

Radio Broadcast Microphones

Radio Corporation of America

RCA

  44-BX - Velocity Ribbon Microphone

RCA introduced the 44 series of velocity ribbon microphones in 1931. It was designed by Harry F. Olson. The 44 became the mainstay of broadcast microphones due to its bi-directional pattern and excellent reproduction. The 44-B series was introduced in 1938 and the 44-BX dates from the 1940s and was produced up into the mid-1950s. Velocity ribbon microphones use a light-weight, metal ribbon (Duralloy) suspended between the poles of a horseshoe magnet (2 magnets on the 44B series.) The motion of the ribbon corresponds to the velocity of the air particles past the ribbon and the voltage generated is an accurate reproduction of the sound wave that transverses the ribbon. The ribbon ends are connected to the primary of a transformer that provides amplification and impedance matching. Also, a reactor (choke) can be inserted via a jumper board in the base of the microphone to compensate for the distance the source is from the microphone. Generally, without compensation (Music Position) requires that the source be at least three feet from the microphone. In V1 (Voice Normal), -10db of low frequency attenuation allows the source to be about 1 ft. from the microphone and for "close talking", V2 gives -22db attn. and allows for a distance of about 7 inches. The frequency response is almost flat from 50Hz to 15KHz (in the Music position, no low frequency attenuation.) The NBC flag shows that this 44-BX was originally used at station KNBC, located in San Francisco, California in the late forties. The prior call was KPO and after a short time, the radio station call KNBC was changed to KNBR, still an active San Francisco radio station.

RCA 

 77-C1 - Directional Ribbon Microphone

RCA introduced the 77 series of all-purpose ribbon microphones in 1932 (designed in 1929) to provide a uni-directional pick-up pattern and wide frequency response. The designer was Harry F. Olson. The early 77 series featured two ribbon microphones in series to create a uni-directional pattern. A switch provided operation of either mike individually or both in series. A labyrinth tube behind the pressure mike's ribbon directed the air movement into sound absorbing material. When using only the pressure mike, the pattern was non-directional. When using only the velocity mike, the pattern was bi-directional. Later, the 77-D series utilized a single ribbon and inserted a moveable shutter assembly between the ribbon and the labyrinth tube which allowed various directional patterns to be realized. Also in the "D" series, a reactor could be placed into the signal path to reduce low frequency response and compensate for "close talking." Frequency response with the 77-C series depended on the directional pattern selected but 50Hz-10KHz was typical. The 77-C1 was only made in 1940 and was replaced with the 77-D, which later evolved into the famous 77-DX. This 77-C1 was used at Reno's radio station, KOH, but eventually it was "dumped" as obsolete equipment (yes, it was found in the dumpster.)

RCA

BK-1A  -  MI-11007  -  Pressure Microphone

RCA introduced the BK-1A Pressure Microphone around 1950. It was a high fidelity, semi-directional dynamic microphone that was especially designed for announcing and remote pickup. It had a smooth response from 60 to 10,000 Hz and it was considered suitable for reproducing both music or speech. It was non-directional when in the vertical position and became semi-directional when used horizontally. The BK-1A was supplied with the output impedance set at 250 ohm Z but the user could change the connections on the internal terminal board and select either 30 ohms Z or 150 ohms Z also. The standard RCA desk stand was the MI-11008 but the BK-1A shown in the photo is mounted on an Atlas stand. This RCA microphone was used at radio station KSL located in Salt Lake City, Utah. The base is marked "KSL Radio Engineering."

Western Electric

Western Electric

  Condenser Microphone - 660

This high quality microphone dates from the mid- 1930s. The condenser type of microphone was used in many radio stations of the twenties (if they could afford them.) By the thirties, other types of quality mikes had replaced the condenser type, (later, this would change back again, with modern, high output condenser mikes.) The response is good, (though directional as the frequency is increased.) The output is extremely low requiring an amplifier to be mounted near by to boost the output to a useable level. This Western Electric 660 features the condenser microphone on top of a two tube amplifier housed in the canister. A five pin connector provides filament and B+ voltages for the amplifier in addition to the +180vdc polarizing voltage between the diaphragm and the back plate. The tubes used are a 76 triode amplifier and a 77 duplex diode/triode tube. The tubes have friction tape wrapped on them probably to reduce microphonics. Also, a phone jack on the backside of the canister allows for an output meter to be connected and the 77's dual diode provides the rectification for the meter. Condenser microphones were also used in sound recording, both for movies or records, in addition to broadcasting.

Western Electric

Cardioid Directional Microphone  639A

The 639A was introduced in 1939 and provided broadcasters with a microphone that could be set to various direction patterns while maintaining high quality performance. Using a velocity ribbon microphone in combination with a dynamic pressure microphone, the 639A offered three selectable patterns. "R" provided a "figure-8" pattern by utilizing just the velocity microphone. "D" selected just the pressure microphone for a non-directional pattern. "C" provided a cardioid pattern by combining the two microphones in series. The selector switch is located on the back of the 639A housing. Frequency response in any setting was 40Hz to 10KHz. An internal transformer provided amplification and impedance matching for the velocity ribbon section. Western Electric also built a "B" version with six selectable pattern settings. In 1941, WE stopped producing the 639 mikes. ALTEC then began producing the 639 series with the ALTEC name on their models. The ALTEC versions were only produced for a few years (as were the WE versions.) The 639A/B was nick-named the "Birdcage" microphone. This particular WE639A was used at the San Francisco shortwave station KGEI (General Electric International), famous as a broadcast/relay station to the Pacific during WWII. 

General Purpose Microphones

Shure Brothers, Inc.

Sidney Shure started in the radio kit parts business in Chicago in 1927. His brother Samuel Shure joined the small company when Sidney changed over to selling microphones but left the company after two years (even though the company was still called Shure "Brothers.") By 1933, Shure was offering their own microphone designs and the business was prospering. During WWII, Shure supplied thousands of their T-17 carbon microphones to the Signal Corps and the Navy. Phonograph cartridges was added to the line of products cumulating in the famous Shure V-15 Mark IV series of high quality cartridges. The company is still a major producer of all types of audio products.

Shure Brothers, Inc.

The "Voice Unidyne"

Model 55 Series

The Shure 55 is a unidirectional, dynamic microphone designed for high quality public address and broadcasting and recording of voice. "Voice Unidynes" were not intended for high fidelity reproduction of music. They were particularly satisfactory as a soloist's microphone, however. Dynamic microphones use a diaphragm that has a voice coil attached. This voice coil can move freely over a pole piece that is mechanically mounted to a permanent magnet. As the diaphragm moves with the varying air pressure (sound) the voice coil moves up and down the pole piece in the magnetic field thus generating a small voltage across the voice coil. The voice coil output is connected to a small transformer that provides a voltage increase and impedance matching. The 55 Voice Unidyne was available as early as 1939 and came in three different impedances, the 55AV was 35-50 ohms, the 55BV was 200-250 ohms and the 55CV was high impedance. Frequency response was generally 40Hz to 10KHz, varying  at the low end with distance from the microphone. The 55 shown is the CV model.

The Shure 55 Voice Unidyne microphone has one of the longest manufacturing histories of any microphone and, since it's still being produced, it's likely to increase it already impressive 70 years of production. The 55 was inducted into the TECnology Hall of Fame in 2002.

Shure Brothers, Inc.

The "Dispatcher"

Model 520-SL

The "Dispatcher" was a rugged, controlled reluctance microphone that was designed for severe field requirements found in amateur radio service, paging use or, as its name suggests, dispatching. Supposedly, the microphone was immune to extreme conditions of temperature or humidity and also provided high output and high speech intelligibility. The green base and mike body are standard as is the robust rear-mounted grip for the push-to-talk function. Selling price was $32.00 in 1950.

Shure Brothers, Inc.

The "Stratoliner"

Model 708S

The "Stratoliner" was introduced in 1940 and was a high-output Crystal microphone. The microphone element used a "grafoil bimorph" unit that was sealed to protect it from moisture or adverse temperature exposure. A filter was also included to prevent damage from excessive RF fields. The element itself features many very small holes in the front which limits distortion and the deep-set mounting which is about one-third back in the body helps with the directivity. Frequency response was around 6000hz down to 60hz with a 2.0 meg ohm terminal resistance. The base is S36A and normally was painted dark gray. The mike body is painted "Iridescent Gray Chrome." The "Stratoliner" was also available for mounting on a floor stand or other type of base and this model was identified as the 708SH.

Shure Brothers, Inc.

The "Sonodyne"

Model 51

The "Sonodyne" was a high quality dynamic microphone that featured a selectable output impedance to allow the end-user to match the microphone to their particular needs for best performance. The element is very large and takes up most of the grille area. The microphone was ruggedly built and performed very well in high moisture areas.

Electro-Voice

Electro-Voice

  Velocity Ribbon Microphone  -  V2

This is Electro-Voice's answer to RCA's 44B series of velocity ribbon microphones. It is much smaller and lighter weight but provided good sound quality at a very reasonable price. The E-V V-2 was available from Montgomery-Wards' "Simplified Sound Systems" 1941 catalog for the bargain price of $20.58, cash, (Mfg.List Price was $35 at the time.) The catalog states that the fidelity is 35Hz-11,000 Hz and that the pattern can be directional or non-directional. Sensitivity was -64db (compared to the 44BX's -55db.) The price was raised to $29.40 (from Wards) after WWII. While the V-2 ribbon mikes may have been used in some of the smaller BC stations, it's more likely that they were mainly for PA applications. 

Electro-Voice

Cardioid Directional Dynamic Microphone

Type 664

The EV-664 was primarily a communications microphone with highly directional characteristics. Utilizing what EV called "Variable D", which was comprised of three sound canceling entrances into cavities at different fixed distances behind the diaphragm providing a front to back spacing that varied in distance (from the diaphragm) inversely with the frequency, the 664 demonstrated a highly directional cardioid pattern. The cavities provided the necessary amplitude and phase conditions to result in a pattern that was constant over a wide frequency range. The directional characteristics of 50% exclusion of side noises and 90% exclusion of rear noises allowed for large distances from the microphone to the source without stray pickup. Dual output impedances of 150 Ohms or Hi-Z and an output of -55db. The 664 sold for $51.00 in 1962 and the optional EV-419 base (shown) was available for $6.00.

Electro-Voice

Dynamic Microphone

Type 638

The EV-638 is a high-quality dynamic microphone designed for communications. The stand features a Push-to-Talk bar in the front that is usually operated with the user's thumb. A locking switch is at the top of the bar.

Astatic Microphone Laboratory, Inc.

The artwork shown on the left is the cover of a 1937 Astatic brochure. Astatic regularly held photo contests for the best photograph that they thought represented the ham operator and Astatic. The winners received $100 but almost all of the entries' photos were eventually used in Astatic's advertising.

The artwork right is inside the 1937 Astatic brochure showing the models available. Note the Youngstown, OH address.

 Pre-1937 Style - 1" thick case and large ID tag

Non-Astatic Stand & Base

Astatic Microphone Laboratory, Inc.

Model D-104

The D-104 Crystal Microphone was introduced in November 1933 for $17.50. Almost instantly, the D-104 became a favorite of AM ham operators for its high frequency response which resulted in very intelligible audio. Its high output voltage was characteristic of crystal elements and its high impedance allowed for direct grid input. The grid shunt resistance should be 5 meg ohms for proper bass response. The early D-104 mikes use a 1" thick case and have a large ID tag along with tapped holes for "ring & spring" mounts. The case thickness was reduced in April 1937 and smaller tags were then used and the ring holes eliminated. Around 1945, Astatic metal tags begin to use the Conneaut location (early tags have Youngstown as the location.) In 1950, an optional piezo-ceramic element was introduced as the D-104C. This model was more durable at the price of lower output voltage. Several Astatic models were offered with either the crystal or ceramic element. The D-104 continued in production with little change until the 1960s when a solid-state amplifier was added to the "UG" stand. In 1976, an eagle and shield was added to the rear cover to commemorate the US bi-centennial. Other variations appeared from time to time until 2001, when production ceased - an incredible 68 years of production.

photo left:  1937 D-104 in the original box. Note the shielded cable that doesn't have any rubber jacket. It appears to be original that way. Also note that the wire ends are spade lugs (difficult to see.) By this time the D-104 price had escalated to $22.50. The 1937 Astatic brochure is shown in other photos in this section.

1937-1944 Style - Thin case, small metal ID tag, Youngstown, OH location

Non-Astatic Stand & Base

Above: The first ad for the D-104 - Nov 1933, QST magazine

Above:  The D-104 with "UG" grip stand, ca: 1960

Right: The back of the 1937 Astatic brochure that provides the specifications of the D-104, K-2 and D-2 mikes. Prices are also provided.

Now, when sound pressure moves the diaphragm, the armature pin transfers the movement to the corner of the crystal wafer. This causes the wafer to flex and because of the piezo-electric nature of Rochelle Salts, a voltage is generated between the two foil plates of the wafer. This voltage appears on the rear terminals of the element. Since the connection is to essentially a capacitor-type device consisting of two foil plates with Rochelle Salt Crystal dielectric, the crystal element has a very high input impedance. Because of the piezo-electric effect, the small movement of the flexing of the wafer can generate a fairly large voltage. Generally, crystal mikes are over 5 meg ohm input Z and are capable of generating about 1 or 2 volts output (maximum) into a high impedance load.

Disadvantages of Crystal mikes are generally that the Rochelle Salts are hygroscopic and can be damaged by excessive moisture. Also, since the wafer is somewhat brittle, mechanical shock can sometimes damage a crystal wafer. The maximum temperature that the Rochelle Salt Crystal can endure is around 125º F so care has to be taken not to leave a mike element in the sun or in a high heat environment. Despite these disadvantages, the Crystal mike is very popular with radio amateurs that are operating vintage tube-type transmitters since a Crystal mike offers high intelligibility, high output levels and very good fidelity (if the transmitter's audio input is a direct-to-grid connection with about 5 meg ohms R as a grid-to-chassis shunt.)

photo above: This is an "all pre-WWII" D-104 mike. The D-104 mike head has the metal tag with Astatic Microphone Laboratory and Youngstown, Ohio. This is the thin case version that was introduced in April 1937. The G Stand base also has a metal tag with Astatic Microphone Laboratory, Youngstown, Ohio. The base is painted "telephone" black which was standard for pre-WWII G stands. Note the dark red felt pad for the sliding grip-bar holder. Later stands used black felt initially and then no felt at all. Also note that the bottom cover has brown felt similar to the brown felt used on telephone equipment. Later stands had black felt on the base bottom cover.

Astatic Microphone Laboratory, Inc., aka: The Astatic Corp.

The  G  Stand (also UG, TUG & TUP)

The G Stand was introduced in January of 1938. The first QST advertisement states that the grip switch only connects and disconnects the microphone. By March 1938, the G Stand ad states that remote relay control is now also a function of the G Stand. The "G" came from "grip-to-talk" as the first few ads referred to the G Stand.

In 1938, virtually all ham transmitters were "homebrew." The majority of hams, including the few hams that operated Phone, were generally using separate transmit and receive antennae. This greatly simplified the Transmit-Receive operation and only required putting the receiver into a standby condition when transmitting. This could be accomplished by using the receiver's front panel standby switch but many receivers also had remote standby circuits that could be actuated by a transmitter's T-R relay. The G Stand could operate the T-R switch which could provide many functions simultaneously. Since the transmitters were all homebrew, the builder decided how he would interface the G Stand to the T-R operation of his station.

Although Astatic ads aren't specific, it's likely that the very first G Stand cable was a single-conductor cable with shield until the remote relay control was added a few months later. Then the standard cable became a two-conductor shielded cable. The G Stand shown in the photo to the left is an example of the D-104 head mounted on the G Stand, both from about 1940. Astatic called the paint used on the base "Telephone Black." Both the mike and the stand have metal Astatic Microphone Laboratory - Youngstown, Ohio tags.

During WWII, Astatic made a G Stand with two cables, one shielded mike cable and one two conductor rubber jacketed cable. Inside the base were two clamps to secure the cables. The exit hole was oblong to accommodate the two cables. Whether this "dual cable" G Stand is standard for WWII, or an anomaly, or if it was an option from Astatic is unknown. Bases were painted gray wrinkle during WWII. After WWII, the base paint was changed to a silver hammertone paint which became the standard base color after that.
 

Astatic Microphone Laboratory, Inc., aka: The Astatic Corp.

Model T-3

Astatic introduced the T-3 Crystal Microphone in the late thirties at a price of $25. The tilting-head was something that the D-104 didn't do and allowed the mike to directly face the user without actually holding the mike. This element was suspended in rubber and placed practically at the front of the body. The T-3's chrome body and small size have endeared it to many users. Later, the T-3 was also available with a ceramic element, the T-3C. Shown is a late T-3C mounted on a TUG-8 amplified base.

Astatic Microphone Laboratory, Inc., aka: The Astatic Corp.

Model 10-D
 

Astatic did offer some dynamic microphones in their line-up. Probably the most popular, at least with hams, was the Model 10-D. Astatic advertised that their 10-D mikes were "tailored response" for the right amount of "sibilance" to provide an intelligible signal. The frequency response was spec'd at 300hz to 3000hz. The input impedance was high at 100K minimum. Additionally, Astatic produced a ceramic element version using the same mike body that was designated as the 10-C. The 10-D could be ordered with the Astatic "UG" Stand for $59.90 or with the F-11 adaptor for a standard desk stand for $39.70. The photo to the left shows the 10-D with F-11 adaptor in its original Astatic box.   

Astatic Microphone Laboratory, Inc., aka: The Astatic Corp.

Model DN

The DN was another dynamic microphone available from Astatic. The frequency response on the DN is much wider than the later 10-D. The DN was available as a Hi-Z mike with the model being the DN-HZ. An internal transformer was mounted at the rear of the housing using black wax. The transformer provided matching from the low impedance voice coil to the specified output impedance and also increased the output level of the microphone. Astatic also produced the DN-50 dynamic mike with optional low impedance versions (250Z ohms and 50Z ohms.) The DN mikes were introduced in 1939 although they had a "venetian-blind" type of grille at that time. The "JT-30-type" grille was added post-WWII and production continued into the early-1950s.

The Turner Company

The Turner Co.

B38   Crystal Microphone

This is an early Turner microphone. The metal tag indicates that Brush Development Company was involved with the element which implies that it is a crystal element. The B38 probably dates from the late-thirties. Note that the mike cable has no rubber jacket (probably not original.)

The Turner Co.

Variable Impedance Dynamic Microphone - U9S

These rugged microphones were popular when the program called for close talking or for use at a windy, outdoor location. Velocity ribbon microphones could be easily damaged from either environment while dynamic microphones were quite durable. Some dynamic mikes will feature a tapped output transformer that allows impedance matching. Generally, one selects the proper terminals via a switch or perhaps by connections on a terminal board in the mike body. In the U9S, the transformer has a selectable output impedance via a switch located on the back of the microphone housing. This U9S is mounted in an interesting NBC flag that doubles as the mounting for the microphone.

The Turner Co.

22D  Dynamic Microphone

The 22D and the 22X were introduced in the 1940s. The "D" was the dynamic version with 200Z/500Z or HiZ impedances available. The early version frequency response was 30hz to 8Khz. Selling price was around $22 at that time. The crystal version used the same housing and was HiZ only. By the early fifties, the 22D was slightly changed in appearance and in the specs. A large etched tag was mounted to the front of the mike base finished in black and red. The frequency response was now 100hz to 9Khz. The optional impedances were 50Z, 200Z and HiZ. Selling price was raised to $40. The 22D shown is mounted on an Atlas stand.

American Microphone Company, Inc.

American Microphone Company, Inc.

C7 - Crystal Microphone

Sometimes we run across really beautiful mikes that just don't have any identification as to the manufacturer. The mike shown to the left is one of those "unknown manufacturer" types. The shape is very "bullet-like" or "aero-style" with decorative fins and concentric circles grille. This probably dates its manufacture to sometime from the late-thirties up to as late as the fifties. The crystal element suggests that it was probably for ham-use or similar non-commercial function. The output connection is via a single button Amphenol standard mike connector. This mike is shown mounted on a general purpose Atlas desk stand.

Does anyone know who manufactured this mike and what its model designation was?

That was how I had this mike described for quite a while. Luckily, I received an e-mail from Dennis Gruenling, who is a mike enthusiast, identifying this beautiful piece as the C7. Thanks, Dennis.

American Microphone Company, Inc.

D6T Dynamic

The D6T was a dynamic microphone that American highly recommended for public address, especially where "stage sound reinforcement" was necessary. The D6T was also recommended for outdoor use in playground and athletic field direction and indoor use with recording along with police and amateur broadcasting. The horizontal or "facing up" of the front of the mike suggests that it was designed to be mounted on a short stand that would allow the user a view "over the top" of the mike while seated at a desk. American stated that speaking directly into the microphone resulted in "clear and commanding speech" that was attributed to the unusual baffle at the front of the mike. The D6T was a high impedance mike at 38K Z ohms and the selling price was $33. There was also a low impedance version at 50Z ohms that sold for $30. Dates from the 1940s into the 1950s.

American Microphone Company, Inc.

D7TP "Clipper"

The "Clipper" was a communications mike that could be used for many applications, from aircraft communications, marine communications or vehicular mobile police or even public address. The D7T is a dynamic mike that was available in many configurations and several different impedances. Generally, the D7T was a high impedance mike while the D7 was a low impedance mike. A TP or TS suffix indicated a "push-to-talk" button on the handle or a "slide switch" on the handle, respectively. The finish is light gold anodized aluminum on the version shown although standard finish was chrome. Selling price was from $24 up to $31 depending on the impedance and other features. Dates from the 1940s into the 1950s.

Take a look at the 1947 movie "Life of Reilly" where William Bendix is using a D7 "Clipper" mike with a PA system that figures in the movie's plot, specifically the "company picnic" scene.

American Microphone Company, Inc.

D4T

Signal Corps U.S. Army

M-2A
 

The D4T was a general purpose dynamic microphone that was designed for a broad range of response, 60hz to 7500hz and a high output level of -56db. The D4T body was very small and quite rugged. The mike could be mounted on a small stand as shown in the photo to the left for desk use or on a floor stand. Since the D4T had the swivel at the base, the angle could be adjusted easily for any type of stand. The D4T was available in Hi Z of 38K or Lo Z of 38-50 ohms. Selling price ranged from $21.50 to $24.00

It wasn't long before the Signal Corps wanted the D4T for some of its applications. Certainly the ruggedness of construction and perhaps the compactness appealed to the Army. When supplied to the Signal Corps the mike was designated as the M-2A. The mike shown in the photo to the left is the military M-2A built by American Microphone Co. on a 1952 contract.

American Microphone Company, Inc.

D33 - Full Vision Dynamic  Microphone

The D33 was a "Full Vision" microphone which meant that because of its small 1" diameter head and thin body it didn't block the view of the artist or audience. Finished in brushed gold and gloss black it was an attractive mike that could be used with the type ND base or could quickly detach from the base and become a hand mike. The D33 was also available in antihalation finish for TV use. There were two audio responses that could be ordered, for AM radio the "Response A" version rolled off at 9khz while "Response B" maintained a fairly flat curve out to 15Khz. The impedance was selectable with the Z switch located under the removable name tag. Lo Z was 30 to 50Z ohms and Hi Z was 250Z ohms which implies that the D33 was almost specifically for broadcasting. Other impedances were available by special order. The D33 selling price was a hefty $125. The D33A shown is in its original velvet-lined carrying case. From about 1950.

Other Manufacturers

Hi-Mound Electro Company, Ltd./Dentsu-Seiki
Trade Names: Calrad, Argonne, Shield, Hi-Mound, Skillman

Type 400C - "Big Walter"

Calrad was one of the many trade names used by the Japanese company Hi-Mound Electro Co, Ltd that was owned by Dentsu-Seiki. Hi-Mound products were generally sold by the electronic catalog dealers such as Allied, Lafayette, B&A, Walter Ashe and many more. The 400 series microphones were physically large crystal microphones. High output levels and robust construction are typical. The 400C features a sound chamber that is felt-lined and then places the microphone element far back in the body. A metal "crossed" divider is mounted in front of the element that creates four chambers directing the sound down to the crystal element. Whether or not this helps the mike's performance for voice is subjective but it does seem to favor use as a harmonica-type mike. In fact, the "harp" players have dubbed the 400C, "Big Walter," in honor of famous "harp" player Big Walter Horton. The Internet video sites host several examples of "Big Walter" being used as a "harp" mike.

Shown in the photos below are three examples of the 400C with different trade names and model numbers on the identification tags. Note the slightly different grille on the Argonne version.

Calrad  400C

           Shield M105

Argonne  AR-54

Carbon Microphones - General Purpose and Military Microphones

Double Button Carbon Microphone

Manufacturer Unknown

Single Button Carbon Microphone

Manufacturer Unknown

"Ring and Spring" Carbon Mikes

Carbon microphones were very popular in  radio broadcast stations in the 1920s. They featured high output but did have the disadvantage of a noticeable "hiss" level. A single-button carbon mike is made up of a stretched diaphragm in contact with  carbon granules contained in a small housing. The pressure of the sound upon the diaphragm changes the pressure that the carbon granules are under, which causes the total resistance of the carbon granules to change. This variable resistance results in a varying voltage across the carbon element when a small bias voltage is applied to one of the mike's terminals. A double-button mike is essentially two small carbon housings on each side of a stretched diaphragm resulting in a "push-pull" type of output. The double-button carbon mike's fidelity was considered equal to the condenser mikes of the 1920s. By the early thirties, the carbon mike was on the way out (except for telephones, hams and the military) and was soon replaced by the velocity ribbon microphone. The "ring and spring" suspension was used to prevent feedback and other noises.

NOTE: While carbon microphones generally are considered to have inferior audio quality and are only suitable for communications, a high-quality carbon microphone (that was designed for broadcast work and is in proper adjustment) will have surprising fidelity. It is unfortunate that nearly all carbon microphones are poor representatives of the technology and its audio capabilities. 

Kellogg for US Army Signal Corps

Single-Button Carbon Microphone  

Type T-32

The T-32 was manufactured for the US Army Signal Corps by Kellogg. The microphone is a single button carbon element that requires a small bias voltage. The bias voltage is supplied by the transmitter or other equipment that the T-32 was used with. Audio reproduction is communications quality. The element can be readily replaced, if necessary. The push-to-talk switch can be used to actuate the equipment that the microphone is to be used with. The T-32 dates from the mid-thirties and was mainly used for military communications up into WWII and commonly used well into the fifties. A very popular microphone with the Signal Corps because of its durability and excellent "carbon mike response."

Shure Bros. for US Army Signal Corps

Single-Button Carbon Microphone

Type T-17 Series

The T-17 Series of military communications microphone was designed by Shure Brothers, Inc. and became one of the most successful microphones used, especially in aircraft. Most T-17 mikes will have three very small holes in the mouth cup which indicates that the mike is a "noise canceling" type, designed for high ambient noise areas such as in a prop-type airplane. Some T-17s were produced with seven larger holes, as the one shown in the photo to the left. These are for use on the ground in a building or in an area that has fairly low ambient noise. The T-17 series has letter suffixes that are for various changes in design. Suffixes A, B and C are two piece bodies with a separate mike element that can be replaced. Suffix D is a one-piece body and features a mike element that is integral to the mouth cup.

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