Hearing Aids

By Roger Russell

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The hearing aids were well designed and sophisticated products. Sonotone manufactured various types of hearing aids. Shown at the left is a 1940 model. The tiny new vacuum tube Sonotone (right) applied the principle of the radio to making hearing easier. Initially, the microphone, amplifier and batteries were in one unit, typically located in a shirt or jacket pocket. A pair of thin wires ran to the receiver in the ear.

Transistors, requiring much less space and current, later allowed for the design of a behind-the-ear unit and then for a complete in-the-ear hearing aid. Later, integrated circuits made it possible to locate the complete unit in the ear canal.


Shown at the right is a later model, the Sonotone 925 hearing aid. This was an all-tube unit measuring 2-5/16" wide, 4-7/16" high and 1-1/8" thick. It weighed 5 ounces without the batteries. The volume control is at the upper right. An on-off switch is at the upper left. It could be placed in a shirt or jacket pocket and held in place with the gold clip. A special strap and cloth holder was also available for women. The microphone was located behind the clip. A double contact socket was at the top of the hearing aid for connection to the receiver.



Sonotone was the first to be in touch with Bell Labs and initiate the use of transistors in hearing aids. In 1953, the Sonotone Model 1010 transistor-tube hearing aid (left) won the first annual Audio Engineering award for technical excellence in hearing aids. It was the transition from tubes to transistors. It used two vacuum tubes in the first stages for high signal-to-noise ratio and one output transistor to conserve battery power. Cost of operation was considerably reduced compared to all tube hearing aids without sacrificing quiet operation. A separate on-off switch and volume control was again used. An accessory microphone and telephone pickup were also available.

The Sonotone 200 (right) was an all transistor hearing aid. It was styled after the earlier 925 tube model (left). In comparison, the 200 measured only 1-7/8" wide, 3-1/16" high and 5/8" thick. It weighed 2.9 ounces without the batteries. The volume control is at the upper right. An on-off switch is on the left side. The switch in the upper left had several functions. In the down position, the hearing aid was in the bifocal mode that dimmed the background sounds in noisy places. In the middle position, the hearing aid was full on. In the up position, the hearing aid could be used as a telephone amplifier. The edge of the telephone earpiece could be placed against the hearing aid and the sound was picked up magnetically. You could then speak into the other end of the receiver.

When the battery cover in the back was open, the battery compartment could be seen at the bottom of the picture. It held one Sonotone 600 battery. Also, the fitting controls are exposed. These can be seen as curved slots across the center of the back. These switches allow adjustment of the frequency response to compensate for individual customer hearing losses.

A complete 16-page owners manual came with the 200 that explained how to use it and had many drawings. It included subjects like how to care for the instrument, the air-conduction receiver, the bone-conduction model, battery installation, how to wear it and how to use it

It could be placed in a shirt or jacket pocket and held in place with the metal clip. A special "Sonowear" pouch suspended from the neck could also be used. The microphone was located behind the clip. A double contact socket was at the top of the hearing aid for connection to the receiver.

In addition, there were hearing aids built into eyeglass frames, which were also available in left and right units for binaural hearing. At the right is the Sonotone 400 eyeglass frame hearing aid with the cover removed. This was an all transistor unit made of lightweight brown plastic. The microphone was located at the rear of the eyeglass frame (left side of the picture). A flip out battery holder was located next to the microphone. The on-off switch was located at the top, about midway. The receiver, located below the switch and inside the 400, connected to a coupling at the bottom of the frame. A soft transparent flexible tube was attached to the coupling and went to the ear and earpiece. The volume control was located towards the front next to the receiver. The whole frame assembly weighed only 22 grams, or about 3/4 of an ounce without the battery. The frame was 3/8" thick for the entire length.

The high-power shirt pocket hearing aids have since been replaced with an equally powerful in-the-ear model. Many of the hearing aids had adjustable frequency bands, like the model 200. Bone conduction units were also manufactured, bypassing the ear canal completely.


Bob’s Virtual Transistor Museum & History Web Site

Known Sonotone models

From “The Hearing Aid: Its Operation and Development” by Kenneth W. Berge, Published by The  National Hearing Aid Society, Livonia, MI. 48152, P281, ISBN 0-911472-02-9




Double Sonotone. Apr.1930. Double mic in tortoise shell case. Monogram “S” in large triangle on front of mic case. Evidently later numbered 300.


60. (Single Sonotone). 1930. Black metal mic 5.7 dia X 1.8 thick mounte battery, with rec and disc vol control.


Tiny Sonotone. 1930. M Metal mic 5.6 dia X 1.6 thick, rec, and disk vol control. May have been renamed "Junior".


200 (Convertible Sonotone). 1932. Double mic in oval molded case 13.OX6.9x 1.5 with small monogram "S" on front. On‑off switch on mic front and soft‑loud on side. Cylindrical vol control. B.C. arid either earphone or rec. Amplifier. Without B.C. and with larger monogram "S" on mic and no on‑off this was called 300. Without amplifier the 300 was called 400. With mother of pearl case model 400 was called 500.


600 (Excel). 1933. Like 200 plus carrycase for mic and batteries.


700 (Radio Aid). B.C. With B.C. and either earphone or rec called 701. Model 700 without B.C. called 702.




33 (Super Sonotone). 1933. A. C. or B. C. Double mic in oval molded case 13.0 X 6.4 X 1.8. Off‑soft‑loud control on side. Opt vertical carry case.


34 (Super Sonotone). Jan. 19,34. Mic 6.4 dia X 1.6 thick. Separate on-off-loud control.


35:1. 1934. A.C. or B.C. Amplifier. mic 6.8 dia X 2.5 thick. Vol control slide at bottom of mic; no holes in front of mic, only a groove opening. Submodel 35:12 had battery plug connector flush with mic. instead of inset.


35:15. Double mic in oval molded case 13. 0 X 6.4 X 2. 1; no holes in front of mic, only a groove opening.


451. Mar. 1937. Mic. 7.5 dia X 2.9 thick; vol control at bottom.


499. 1938? Mic in oval molded case 13.3 x 6.4 X 1. 8. Off‑soft‑loud control on side of mic.


505. Sept. 1938. M ic 7.5 dia. Rec. Amplifier.


444. Feb. 1939. M ic 6.8 dia X 2.4 thick. A. C. or B. C. Vol control on lower front of mic.


Vacuum Tube


Portable Table Model. 1935? 2VT, ac. Case 21.7 X 14. 0 X 17.4. Double carbon inic inside at end of case B.C.


485 (Perceptron). 1937. 3VT, in case like folding camera of that era, with shoulder strap. Crystal mic. Crystal and magnetic rec. 23.9 x 12. 1 x 4.8.


520. Sept. 1939. 2VT, 2‑piece. Crystal mic A.C. or B.C. 12. 7 x 6. 2 x 2.5.


530. 1911? VT 2‑piece. A.C. 9.5 X 4.8 x 2. 1.


531. 1942. 2VT, 2‑piece. A.C. or B.C. 10.2 x 5.4 x 2. 1.


533. 1942. VT, 2‑piece. 12.7 X 6.2 X 2.5.


600. 1945? VT, 2‑piece. 10. 0 x 6.8 x 2.4. Submodel 70OX had battery area attached at bottom to make it 1‑piece. 14.9 X 6.8 X 2.4.


900. Sept. 1947. VT, I‑piece. 3‑position TC. Front case rhodiurn finish metal and back gray plastic 12. 1 x 6.5 x 2.5. Could also be worn 2‑piece.


50. 1948. Professional Table Set. ac or de. Metal case 16.5 x 11.5 x 11.4.


910. 1949. VT, I ‑piece. 9.4 X 5.7 X 2. 1.


920. 1949. VT, 1‑piece. Gray‑green and silver case 10.8 X 5.7 x 2. 1.


925. 1950? Same case as 920 but in cinnamon arid silver.


940. 1950. VT, I‑piece. Opt ext mic. 8.7 X 3.0 X 1.9.


966. 1950. 6vr, I‑piece. 11.9 X 6.2 X 2.5. Also available as 2‑piece.


977. 1951. VT, I‑piece. TEL. AGC. 8.7 x 5.4 x 2. 1.


988. 1952. VT, I‑piece. Opt ext mic. TEL. Metal case.


1010. Dec. 1952. 2VT & IT. Opt ext mic. TEL. Same case as 988. Won the First Annual Audio Engineering Award for technical excellence in the design and manufacture of hearing aids. One of the 1st if not the 1st aid with a T.


Body Transistor


1111. 1953. 3T. 122. 7.6 X 4.5 X 1.6. Based on patent #2,789,160 by Franklin A. Gage.


1200. 1954. 4T. TEL. 1.3/2.6/3.9 volts. Aluminum case.


1000. (Golden). 1961. 6T, PP. TEL. AGC. 401(2).


22. 1962. 6T, PP, TEL. AGC. 401(2).


45. Jan. 1968. 4T. 625. Case like 100.


77. June 1959. 6T. TEL. 401. 5.4 x 3.5 x 1. 6.


88. June 1959. 6T. 401(2). Circuit like 77. 5.9 X 3.5 X 1.6.


99. June 1959. 6T. 401(4). 8.9 x 3.5 x 1. 6.


100. June 1955. 4T. 625. Metal case 5.4 X 3.5 X 1.4. M ic opening 6 small horizontal holes. Modified with 2 additional mic openings and new vol control.


200. June 1956. 4T, PP. AGC. TEL. 122. 7.6x4.5x 1.6. Submodels: C (B.C.), E (A. C.) and X (high power).


300   1964. 6T, PP. Ceramic top mic. TEL, AGC. 401. Submodels: C (B.C.), E (A.C.) and X (two 401). May be 1st hearing aid with ceramic mic.


600 1967 5T, PP. Ceramic top mic. TEL. AGC, 401. Stainless steel case 6. 6 X 3.5 X 1. 8.


60OX. 1967. 5T, PP. TEL. AGC. 401(2). 8.8 x 3.5 x 1. 8.


612. 1975. Ceramic mic. TEL. AGC. 401. Submodel 612X.


670.  1972. 10T, PP, Top ceramic mic. 933. Silver case. Submodels. B (basic model), T (TEL, NIT. AGC.), S (TEL, NIT. AGC. Input control, output regulation), X (extra power), and XV Has four internal 3-position selector switches (X with LFE).




25 Mighty Wisp). 1963. 4T. AGC. 575.


36. 1972. Ceramic mic. 13. Submodels: 36‑13, 36‑21, 36‑21‑B2 (electret mic. CROS), 36‑22 (1973), and 36‑23 (1973. Electret mic. AGC.)


37 (Micro Wisp). Jan. 1969. IC, 3T. 13.


55 (Wisp). June 1961. 3T. 575. Modified as 58 in 1968 without separate on‑off switch and smaller mic opening.


70 (Sono‑Wisp). May 1965. 3T. S 13.


72. 1966. 4T. Automatic TEL. S76.


76. 1967. IC, 3T. S13. Case like 70 but front mic, and vol control to rear.


77. 1971. Front mic. TEL. S76. Submodels: S (ceramic mic), P (1973. Electret mic), and D (Ceramic or electret directional mic).


79. June 1955. Barrette or BTE, ext rec. 3T. 625. Plastic case 4.6 x 3.2 x 1.6. May be the first BTE aid.


80. 1970. IC, PP. Front mic. 675. Submodels: B (basic), A AGC T (TEL), arid S (Universal. AGC and TEL. Internal TC).


333. Feb. 1957. BTE or barrette. 4T. 400. Metal case 3.2 x 2.1 x 1.3 Based on patent #2,938,O83 in 1960 by Frank A. Herrmann.




35. 1966. 4T. Automatic TEI. S76.


40. 1970. ‑IT. TEL. AGC. 675. Submodel 40‑6 in 1973.


50. 1972. Opt CROS arid TEL. 41.


66. 1960. 3T. AGC. 675. Submodel styles: 66E attached to EG and 66T BTE.


75. (Thinline). 1964. 4T. 312. Modified 1972 as 75‑2 (Thinline 11) with IC, 3T. TEL. 312.


400. Sept. 1957. 4T. AGC. 67 5. 1.8 x 1. 1.


410. Sept. 1958. 675. 1.8 X 1.4. Submodel styles E (EG) and T ("Tuck‑A‑Way" BTE).


430E (Sovereign). 1961. 4T. TEL. 675.


500. Sept. 1957. Like 400 but B.C. 1.7 X 1.4. One of the Ist if not the 1st B.C. EG aid.


40‑P. 1976. S76.


At-Ear and In-Ear


33 (Sonet). Jan. 1966. In‑ear. IC, 3T. 212. 3‑hole mic opening.


34 (Sonette). 1970. Like 44 with 312 arid 2‑hole mic opening.


44 (Wisp Ear). 1962. 1 n‑ear. 3T. 312. Metal case.


222. Feb. 1957. At‑ear. 3T. Metal case 2. 0 X 2.1 X 2.2. Based on patent #2,938,083 by Frank A. Herrmann.


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