Radio Boulevard
Western Historic Radio Museum

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~ Vintage Radio Broadcast and Communications Microphones ~

~ Vintage Radio Broadcasting Equipment ~
 

The First Radio Broadcast
 Reginald Fessenden first transmitted voice in 1900 using a spark transmitter but the audio quality was not commercially useable due to distortion from the poor quality of the carrier wave. As early as 1903, Fessenden had been experimenting with mechanical transmitters - high frequency alternators - as a source of a pure continuous wave carrier for voice transmissions. NESCO (National Electric Signaling Company) was formed to finance Fessenden's research and his high frequency alternators were built by General Electric. In Dec.1906, Fessenden received a high frequency (50kc) alternator from GE that was designed by Ernst Alexanderson. By inserting a water-cooled carbon microphone into the antenna feed, Fessenden could voice modulate the alternator's output. The system was demonstrated on December 21, 1906. Fessenden then decided to test broadcast a short voice and music program on Christmas Eve. The broadcast consisted of violin music (played by Fessenden) and recitation of Bible passages. Though the program was a test, it was picked up by some shipboard radio operators around Cape Cod, Massachusetts. Fessenden repeated the broadcast program on New Year's Eve, 1906. At the time, very little was mentioned of Fessenden's two pioneer broadcasts and they were almost forgotten. However, letters from Fessenden preserved the experiment which is now considered one of the important events in radio history. Though Fessenden had successfully demonstrated the concept of broadcasting, he was actually more interested in providing point-to-point voice communications and, as a scientist, he preferred to continue on with this and his other radio developments and inventions. He eventually retired to Bermuda.


 
Dr. Reginald A. Fessenden  ca:1926, from "Every Man's Guide to Radio"

Vintage Microphones
 

Radio Broadcast Microphones

 

Radio Corporation of America

RCA was created by General Electric in 1919 using some of GE assets and primarily by the purchase of American Marconi. RCA was destined by its very creation to dominate the Radio Industry. GE maintained some control over RCA during the 1920s but the 1930 Anti-trust Suit gave RCA total control of the Radio Industry. Radio Broadcasting was just one of the many divisions of RCA and, with its ownership of NBC, along with producing all types of Radio Broadcasting equipment, installation, maintenance, recording,...on and on,...RCA was the dominate force in Radio Broadcasting for decades.

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 for sometime at Reno's radio station, KOH, but eventually it was "dumped" as obsolete equipment.

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 was the manufacturing division of AT&T. During the 1920s, AT&T owned most of the vacuum tube patents and was cross-licensed with General Electric, Westinghouse and RCA to allow shared patent use by those companies at the exclusion of other companies. At the beginning of commercial radio broadcasting, Western Electric wanted to be the dominate company and build, supply and control all of the equipment used in the fledgling industry. That lasted through the twenties but RCA came on strong from 1930 on. Western Electric equipment was also used in sound-on-film movies, electric recording technology and telecommunications.

 

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 (or monitor) 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 1938 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, ALTEC began producing the 639 series with the ALTEC name on their models. 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

The General Purpose Microphone had a variety of uses from Radio Broadcasting for the higher quality types to public address, professional or amateur communications or vocal-musical recording. These microphones usually have the capability of selecting various impedances to better match the end users specific needs. Also, some designs provided for higher durability or for pick-up patterns that favored public address or live performance. Crystal microphones were primarily for the radio amateur and featured high output impedance and high output levels. The carbon microphones were favored by the military for their ruggedness and high output level.

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

In South Bend, Indiana, two fellows, Lou Burroughs and Al Kahn, decided to go into the radio repair business. The year was 1927 but by June 1, 1930, they had formed Electro-Voice to produce microphones. Burroughs left for a short time, which left Kahn as the sole-owner. By the mid-thirties E-V was adding employees and producing very successful microphones. Burroughs returned in 1936 but as Chief Engineer this time. E-V produced very popular microphones over the years and even became owner of Radio Manufacturing Engineers (RME) for awhile. Nowadays EV is part of the Telex Corp. and Bosch Security.

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 E-V 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.

Astatic Microphone Laboratory, Inc. was founded in 1933 by two hams, C.M. Chorpening, W8WR (later W8MJM) and F.H. Woodworth, W8AHW. The two hams experimented with different types of microphones for their AM ham stations beginning in 1930. Their mutual friend, Charles Semple, worked for Brush Development Co. where he had been experimenting with Rochelle Salts crystals. Semple demonstrated some crystal pick-ups that Brush was working with and Chorpening and Woodworth recognized that a crystal microphone would provide excellent service in their AM ham transmitters. When Astatic was incorporated, in 1933, Semple was brought into the company as general manager. Astatic was originally located in Youngstown, OH but moved during WWII (late 1944) to Conneaut, OH. After WWII, Astatic Microphone Laboratory became The Astatic Corporation. After a series of different owners in the late-nineties and early 2000s, Astatic is no longer in business.

 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 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. The "grip" switch stand ("G" Stand) was introduced in January 1938 but didn't become popular until much later. The early "G" stand bases are gloss black with metal ID tag. In the fifties an optional piezo-ceramic element was introduced as the D-104C. This model was more durable at the price of lower output voltage. The D-104 continued in production with little change until the 1960s when a solid-state amplifier was added to the "G" 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 after the first D-104 was offered.

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

Non-Astatic Stand & Base


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

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

 

Far right: Astatic flyer for their microphones in the late thirties

 

The Crystal Microphone - How it Works - The construction of a crystal microphone begins with a layer "sandwich" that consists of a layer of foil, a layer of Rochelle Salt Crystal followed by another layer of foil. This "sandwich" is cured until the Rochelle Salt Crystals are structurally sound and then the "sandwich" is cut into small, generally rectangular pieces. The small sandwich-wafer is now mounted in the element housing by gluing three of the four corners to mounts inside the element. To each foil plate a wire is connected and these two wires are connected to the rear terminals on the element housing. To the remaining non-mounted corner of the wafer an armature pin is glued. The other end of the armature pin is mounted to the center of the diaphragm. The diaphragm is glued around its perimeter to the element housing. This completes the assembly of the crystal element.

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.)

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 as a grid-to-chassis shunt.)

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 came with a ceramic element, the T-3C. Shown is a late T-3C mounted on a TUG-8 amplified base.

 

The Turner Company

David Turner started building PA systems for funeral homes in the late twenties. He built his first PA in a closet in his father's Cedar Rapids, Iowa funeral parlor. By 1931, microphone manufacturing was added but so was a new Pressure-Embalming Machine manufacturing business. Tuner's business combined embalming machines and supplying sound systems mostly to the funeral homes. Gradually the microphone business grew and came to include supplying microphones to radio amateurs and manufacturing microphones for some military contracts during WWII. The Embalming Machine business also continued on and today is the largest supplier in that field. In 1967, Conrac purchased microphone division of The Turner Company and, by 1979, it was owned by Telex.

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.

 

Other Manufacturers

Calrad,  aka: Argonne

Type 400C - "Big Walter"

Calrad was a Japanese company that sold many types of electronic products under several different names. The most often seen other name is Argonne. 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.

 

Carbon Microphones - General Purpose and Military Microphones

If ever a type of microphone is the subject of endless criticism, it's the Carbon Microphone (CM.) As one of the first concepts at how to build a sound transducer certainly the CM has been around since the nineteenth century. In that length of time the CM has seen duty as the earliest of radio broadcast microphones, the earliest of telephone microphones and the earliest of military communications microphones. Except for the radio broadcasting types, the other CMs were designed for communication - not high fidelity. Since most military uses were in high noise areas, their CMs were mainly of a "noise canceling" design which has led many to believe that all military CMs require a voice projection that is just short of screaming and even then they produce inadequate output to properly modulate a transmitter. CMs were popular for two reasons. First, they are robust and can take a lot of physical abuse and still function fine. In fact, the myth that a carbon mike sounds best after "beating it on the table" has some basis in practical experience. Second, when in good condition they have a high output that is based on the bias voltage level supplied. Most military CMs were designed for quick and easy repairs by way of a replaceable mike element and consequently the mechanical design of a small easy-to-remove element somewhat limited the performance. When designed for quality Radio Broadcasting, the CM is built substantially better than the military mikes. Gold plated diaphragms are used along with felt protectors on the carbon cups. Large opening allow for good fidelity with high output. The only disadvantage is a noticeable "hiss" that is apparent in all CMs. Having heard a recording made with a rebuilt Western Electric 1A microphone, I can say that a quality BC type CM will surprise even the most ardent CM critics at the fidelity and quality that can be achieved. Remember, nearly all CMs that you might encounter are poor representatives of what the technology was (or is) capable of.

Double Button Carbon Microphone

Manufacturer Unknown

carbmic.jpg (16969 bytes)

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 late twenties and was mainly used for military communications up to WWII and commonly used well into the fifties. A very popular microphone with the Signal Corps.

 

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.

Other Carbon Mikes

Shown to the left is the M-85/U carbon mike that was used mainly by the Navy. The small handheld mikes had the PTT button on top and were "noise canceling."

Shown to the right is a carbon mike made by Universal Microphone Company, Ltd. The instructions are embossed on the front of the mike, "SPEAK LOUD AND CLEAR - LIPS TOUCHING." The clips that can be seen at the back of mike body are part of the mounting bracket that is still present with this early microphone.


 

Radio Broadcasting Equipment

Gates Radio Company

Henry Gates started in the radio business in 1922 but his son, Parker Gates, decided to go into the Radio Broadcasting Equipment business instead. This successful decision put the Gates' name as one of the most popular of the Broadcast Transmitter and Monitor suppliers. Gates was located in Quincy, Illinois. The company was purchased by Harrison in the late fifties and most of the equipment was "cheapened" to the point where Gates was referred to a "The Quincy Garbage Can."

photo above: The BC-250L is "ON" in the photo, output of 250W into the dummy load in the rack. Note the lamps, the meter readings and the tube filaments.

Gates Radio Company

AM Broadcast Transmitter  BC-250L 

KOWL - 1490 KC - Lake Tahoe

 

This is the original, first transmitter used at the AM radio station KOWL 1490 KC located at Lake Tahoe. KOWL went on the air in 1956 with this Gates BC-250L "Hi-Watter" AM transmitter running 250 watts. The original studios for KOWL were located at Harrah's Club at Stateline, Nevada although the transmitter shack and antenna were located about two miles south in the city of South Lake Tahoe, California. With the Harrah's location, many of the major entertainers that played Harrah's in the fifties and sixties ended up being interviewed on KOWL, their voices going out over the airwaves via this transmitter. The transmitter was in continuous operation from 1956 until the late-sixties, 24 hours a day, seven days a week. It was placed as a stand-by unit in the late sixties and the last time it was powered at KOWL was in 1993. We removed the BC-250L from the original KOWL transmitter shack on August 8, 2007. It had resided in that same building from 1956 until 2007 when we then moved it to Virginia City. The BC-250L uses two 810 tubes as RF amplifiers and two more 810 tubes as modulators. It is a high-level plate modulated transmitter that weighs in at around 800 lbs. The dimensions are 78" tall by 42" wide and 31" deep.


photo above: The original sign from Harrah's Club at Stateline, Nevada where the KOWL studio and offices were located.

The rack to the right of the transmitter contains some of the monitoring equipment that was used with the KOWL BC-250L. The following are close-up photos of the KOWL equipment the I have. The Gates MO-2639 AM Modulation Monitor is from 1956. The large "PEAK INDICATOR" would flash anytime the preset modulation percentage was exceeded. 

The 1956 Gates MO-2890 Frequency Monitor was used to accurately monitor the transmitter's carrier frequency and show any deviation from 1490 KC. The frequency accuracy had to be maintained to 20 cycles or less.

The Gates Amplifier M-2996-A provided some compression to the audio signal to the transmitter for higher "talk" power.

The Gates "STA-LEVEL" is an automatic audio level device that works like an AGC circuit to keep the high peak levels low and to bring the low levels up. Helps keep the modulation level to the transmitter more consistant.

The Gates Stereo Yard is the console from the later KOWL station - still KOWL, but this board wasn't used with the BC-250L. The Yard Power Supplies are also shown.

The SC-101 Spot Tape Player was used to store and playback 101 "spots" (usually commercials) selected by the sliding the level to the appropriately numbered "spot."

Also shown is the original KOWL sign that was at Harrah's Club in the 1950s-1960s. This sign is now hanging in our shop with the transmitter and monitoring gear.

Above: Gates MO-2639 AM Modulation Monitor from KOWL. Original to 1956 set-up

Above: Gates M-2996-A Amplifier-Compressor from KOWL. Original to 1956 set-up

 

Right: Gates MO-2890 Frequency Monitor from KOWL. Original to 1956 set-up

Right: Gates M-5167 "STA-LEVEL." Original to 1956 set-up 

Left: Gates Stereo Yard Console from KOWL (later vintage)

 

Above: Power Supplies for the Stereo Yard. Model 994-5548-007 from KOWL (later vintage)

Above: Gates SP-101 Spot Tape Player from KOWL. Original to 1956 set up

For the complete story of how we moved the Gates BC-250L from South Lake Tahoe, California to Virginia City, Nevada in August 2007 (when it was donated to our museum) go to the webpage "KOWL's Gates BC-250L AM BC Transmitter - Moving and Restoration" - Navigation link below in the index. Also, we will be adding a section on the subsequent move of the KOWL transmitter from Virginia City to its new home in Dayton, Nevada (August 2013) - coming soon.
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Gates Radio Company

AM Modulation Monitor   -  Model M-5693

The Gates M-5693 Modulation Monitor uses a plug-in coil to set the input frequency range for the Carrier Meter circuit. The Carrier Meter would be set to 100 (with no transmitter modulation and after peaking the monitor frequency control) then the Modulation Meter (right) would readout the transmitter modulation level and relative db level. A selector switch allowed either negative or positive peaks to be read. The Neg Peaks lamp would flash if negative cutoff was detected, depending upon what modulation percentage level was selected (with 100% being maximum.) Audio output (for headphones) and quality output monitoring (for distortion analyzers) were also provided. RF input was usually from a small pick-up coil near the tank circuit in the transmitter or near the antenna. The M-5693 dates from about 1959. Not from KOWL, this M-5693 was found in a storage unit in Dayton, Nevada several years ago.

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Gates Radio Company

Transcription Turntable - Model MO-2705A, Type CB-11

Initially, the CB-11 was a standard, two-speed machine (78RPM and 33.3RPM) but as 45RPM records became more popular the new models had the platter modified with two large holes. These provided access to the capstan and allowed the user to install an internally slotted sleeve over the 33.3RPM part of the capstan, which was now also slotted on top, thus locking the sleeve and increasing the capstan diameter which increased the turntable speed to 45RPM. This CB-11 is fitted with a Gray Research Tone Arm with a GE VR cartridge with 3mil stylus for 78RPM records. Not from KOWL, this CB-11 was found at a garage sale in Carson City, Nevada around 1990.

 

Radio Corporation of America

RCA

308-B Field Intensity Meter

Field Intensity Meters are devices for measuring a radio signal's electromagnetic intensity at a distance. The measurement would be expressed in microvolts or millivolts per meter which indicates what the signal intensity level is compared to the amount necessary to generate the same level in a conductor one meter long. There are also factors such as antenna height at the transmitter that enter into the measurement. The 308-B is essentially a wide range radio receiver that tunes from 117kc up to 18mc in six tuning ranges. Meter readouts allow for accurate measurement of the signal intensity. Specific antennas are used per frequency range and are plugged in a receptacle that is accessed from the top of the cabinet. A portable power pack plugs into the socket located at the rear of the cabinet. Field Intensity Meters were used to plot antenna patterns and signal coverage of a transmitting station - all measurements that had to made at a distance from the transmitting antenna. The lid contains the various antennas and cables along with charts and manual. The lid was removed for the photograph.

RCA

70-D Transcription Turntable

This is the RCA Type 70-D, Model MI-11801,  Transcription Turntable with RCA Type 72-D, Model MI-11852 Recording Attachment. This piece of equipment was used in broadcast stations for playing records and for recording onto transcription discs for future playback. Speeds available were 78RPM and 33.3RPM. Also included inside the base is a MI-4975 Reproducing Filter network. The recording attachment allows the user to select groove density and direction (outside-in or inside-out.) There is a scale showing remaining time on a particular recording disc. Ample storage in the base which also houses the large motor and flywheel. This turntable dates from the late forties and was one time used at station KRON-TV (though this might just be somekind of property tag.)

RCA - "ON AIR" Warning Light from KNEV

This light was part of the original station equipment at Nevada's first "successful" FM station, KNEV, owned by Jerry Cobb (shown in photo with KNEV microphone.)  Actually, the first FM station in Nevada was KWRN, which was partially owned by the Reno Gazette newspaper. Spending $250,000 for the transmitter, antenna, a modern studio and control room, KWRN went on the air on November 27, 1947. The transmitter was moved to a building that had been built on Peavine Mountain in 1948. The Gazette really never promoted FM's advantages and merely rebroadcast what was already on the local AM stations. The Reno listeners had no reason to switch to FM. With little revenue coming in, it was decided to shut down operation of KWRN on April 15, 1950. The equipment was sold to the Bell Telephone Co. of Nevada. Jerry Cobb purchased the equipment from the telephone company while it was still up on Peavine Mountain. The windows of the transmitter building had been broken and the door left open. Most of the equipment had been vandalized. Salvaging everything, Jerry and his son, Neal, moved the equipment to their home at 1260 Ridgeway Ct., in Reno. Jerry actually had to locate the final RF amp tubes, which had made their way to a fireplace mantel in Central California. By 1951, Jerry had rebuilt the station and had it operational in his garage, however the neighbors were concerned that the FM signal would be "picked-up" by their appliances. Jerry moved the station to 538 So. Virginia St., obtained the license and, with the call KNEV, went "on the air" on Christmas Day, 1953. Jerry Cobb enthusiastically promoted FM by giving away "FM only" receivers to all of the "big shots" in Reno. Additionally, by featuring fine music and hosting several creative programs with man-on-the-street interviews (which he had developed when working at KOH), Cobb got the public's attention and they started buying FM radios, making KNEV and FM a success in Nevada.

 

Western Electric

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Western Electric

45-A  Amplifier

This input/output transformer coupled, single-ended amplifier uses two WE 205-D triodes, one as an audio amplifier and the second as a B+ voltage rectifier. The 45-A dates from about 1930 and this particular one was used by the Bell Telephone Company of Nevada (later Nevada Bell) for an in-line amplifier when remote site broadcasts required using the telephone lines to send the audio signal to the radio broadcast station transmitter. The amplifier also provides various B+ voltages to operate auxiliary equipment. Powered by 110vac.

 

General Radio Co.

 

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General Radio Co.

Modulation Monitor - Model 731-A

AM Radio Broadcast stations were required to monitor the percent of modulation of their transmitter. Most modulation monitors were designed to comply with specific FCC regulations which stated the necessary requirements. The General Radio 731-A Modulation Monitor dates from about 1938. A variable capacitor tunes a pick-up inductor mounted near the tank coil of the broadcast transmitter. This input is then detected to drive the Carrier Meter. Regulated power supplies deliver reference voltages that compare the detected signal/lp filter output and give a percentage of modulation readout. Another circuit allows a variable setting of an Over Modulation warning lamp. Outputs for monitoring are accessed via a Jones Plug on the rear panel. The operator can select Positive or Negative Peaks for readout on the modulation meter.

General Radio Co.

Beat Frequency Audio Oscillator

This piece of test gear allowed the user to select any frequency from 20hz up to 20Khz with just the turn of one dial. No range switches or multiple scales to read - all frequencies covered in one sweep of the dial. The circuit that made this wide range possible used a variable frequency oscillator that heterodyned against a fixed frequency oscillator. Due to the "mixing" of the two frequencies a "beat frequency" was created that allowed the wide range of frequency coverage using only a single range and a single scale dial. Additional circuitry provided accurate output measurement and level control. A precision piece of equipment that was used in the lab but also in broadcasting where a precision audio oscillator was necessary for testing and set up of the transmitter.

 

Other Manufacturers and Equipment

Earle C. Anthony, Inc. - KFI

KAIH - Portable 25W Transmitter

Earle C. Anthony was a well known automobile dealer in Los Angeles, California and owner of radio station, KFI. This is the 25 Watt Portable Transmitter licensed as, KAIH. It was used in 1941 to provide "live", two-way wireless communication between KAIH (at a remote location) and KFI. The listener would hear the KFI broadcast with short, live inserts from the remote site. June 9, 1941 was its first use, operating from the roof of the Turf Club in Inglewood, CA, reporting on an aviation strike. The KAIH transmitter ran on batteries, operated on the 2.0-3.5Mhz band (crystal controlled and selectable from five different xtal frequencies.) and used a 30 foot portable antenna. The circuit uses an 807 modulated by 6L6s. Designed and built at the KFI shop.

Capitol Records

45RPM  Cue Disc

This 12 inch in diameter disc was used to adapt a 45RPM single to a transcription turntable and allow the DJ to "cue-up" the record. The cue disc is made of the same kind of material used for 78RPM records. The edge is embossed with ridges for the DJ to grip the cue disc and allow it to "slip" on the felt of the rotating turntable. Releasing the cue disc let the 45RPM single come up to speed fast and begin playing quickly. When finished, the finger-sized depression made for easy removal of the 45RPM record. Dates from the 1950s.

Henry Rogers/Western Historic Radio Museum © 2012

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Website Navigation Index

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Western Historic Radio Museum - Information
 
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2007 Move from Lake Tahoe - Restoration - PLUS -  2013 Move to Dayton, Nevada & Getting on 160M 

 

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M.H. Dodd's 1912 Wireless Station
100th Anniversary  Edition 
Includes New Photos, Reassembly Info and Lots of Original Vintage 1912 B&W Photos + Reassembly in Dayton

 THE COLIN B. KENNEDY COMPANY
"RADIO APPARATUS OF QUALITY"
Universal, Intermediate Wave and Short Wave Models History, Restoration and Operation - Lots of Photos

A.H. GREBE & CO., INC.
"A Guide to the Synchrophase MU-1"
Comprehensive Manufacturing History, Restoration, Neutralizing, Performance Information - Lots of Photos

 

 SE-1420, IP-501 & IP-501A
"The Classic Shipboard Wireless Receivers"
Comprehensive History, Restoration and Operation Info - Tuning in NDBs with IP-501-A

Vintage Long Wave Receivers
Long Wave Receiver Profiles, Loop Antenna Info, NDB Info and Log,
Fallon NV "Master - M" Loran Station Tour

 

 

- Vintage Communications & Amateur Radio Equipment  ~  Full Length Articles with Photos -

National Co. - HRO Receiver
"The Cream of the Crop" 
Expanded Edition - Comprehensive History, Serial Numbers, Restoration, Lots of Photos & More

 National Co. - NC-100 Series
"Moving Coil"  Receivers 
Comprehensive History, Serial Numbers, Restoration & More - Includes Civilian Versions, Military Versions & Airport Versions

Hallicrafters SX-28
"A Pre-war Masterpiece"

Comprehensive History, Serial Number Analysis, Restoration Details & More

Hallicrafters DD-1 "Skyrider Diversity"
Comprehensive History, Serial Numbers & Restoration Details

RCA's Legendary AR-60 Receiver
Comprehensive History, Serial Number Analysis, Restoration Details & More - including the AR-60 connection to Amelia Earhart's Disappearance.        

RCA's Amazing AR-88 Receivers
Comprehensive History, Restoration Info, How to do IF Sweep Alignments, Serial Numbers & More

 Hammarlund Mfg.Co.,Inc
The Incredible Pre-War 'Super-Pro'
Comprehensive History, Serial Number Analysis, Restoration Details. Includes info on the Hammarlund Comet Pro

Hallicrafters' "Super-Pro" R-274 Receiver
Comparison of the SP-600 to the R-274(SX-73) in detail, best features of each. VOTE for your favorite Super Pro

 

-  Rebuilding Communications Equipment  ~  Full Length Articles with Photos -

Rebuilding and Operating the AN/GRC-19
T-195 XMTR & R-392 RCVR
 Detailed Information with Lots of Photos

Rebuilding the R-390A Receiver
Detailed Restoration Information with Lots of Photos

Rebuilding the ART-13 Transmitter
Detailed Restoration Info with Lots of Photos

Rebuilding the Hammarlund SP-600
Detailed Restoration Information with Lots of Photos

     Rebuilding the Collins 51J Series Receivers
NEW!  
Detailed Restoration Information with Lots of Photos - Includes R-388 Receiver
Successfully Operating the BC-375 on the Ham Bands Today
Detailed Information on Power Set-ups that Work, Dynamic Neutralization, BC-191 Info & More 
Rebuilding the BC-348 Receiver
Detailed Information on all BC-348 Types, Dynamotor Retrofit Information, AC Power Supply Enhancement - Lots of Photos
Building an Authentic 1937 Ham Station
Utah Radio Products - UAT-1 Transmitter

 

- WHRM Radio Photo Galleries with Text -

Entertainment Radios from 1922 to 1950

Roaring 20s Radios
1922 to 1929

Vintage Table Radios
1930 to 1950

Floor Model Radios (Consoles)
1929 to 1939

Only Zenith Radios
1930 to 1940

Communications Equipment from 1909 to 1959 - Commercial, Military & Amateur

 Early Ham & Commercial Wireless Gear
1909 to 1927

Classic Pre-WWII Ham Gear
1928 to 1941

WWII Communications Equipment
 U.S. Navy & U.S. Army Signal Corps  1941 to 1945

Commercial & Military
Communications Gear
1932-1941 & 1946-1959

Post-WWII Ham Gear
1946 to 1959

Vintage Broadcast Equipment, RTTY & Telegraph Keys

Vintage Microphones
 & Vintage Broadcast Gear
1930 to 1950s

Radio Teletype - RTTY - with Real Machines
includes TTY Machines, Military TUs and Amateur TUs

Telegraph Keys - 1900 to 1955
"From Straight Keys to Bugs"
Hand Keys and Semi-Automatic Telegraph Keys

 

 

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Entertainment Radios For Sale

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 Radio Boulevard
Western Historic Radio Museum

 Vintage Radio Communication Equipment Rebuilding & Restoration Articles,

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1909 - 1959

 

 

This website created and maintained by: Henry Rogers - Radio Boulevard, Western Historic Radio Museum 1997/2014