Body-Style Transistor  Hearing Aids—General Information

While the vacuum tube, which had been employed in hearing aids since the early 1920s, was a major advance in improving the amount of amplification available in hearing aids, further miniaturization from that achieved by 1950 was not possible because of the need for two relatively large batteries to power the hearing aids.

This changed when the people at the Bell Labs invented the transistor in 1948. Hearing aid manufacturers quickly realized that the transistor represented the future of hearing aids. The transistor eliminated the need for the "A" battery to power the filaments of the vacuum tubes, and the "B" battery to power their plates. Furthermore, the lower operating voltage required by transistors over that of vacuum tubes meant that a single smaller battery was all that was required.

The First Step—Hybrid Vacuum Tube/ Transistor Hearing Aids

This changed when the people at the Bell Labs invented the transistor in 1948. Hearing aid manufacturers quickly realized that the transistor represented the future of hearing aids. In fact, hearing aids were the first commercial application to use transistors.

By substituting a transistor for one of the three vacuum tubes, filament current drain was reduced by 1/3 resulting in slightly longer battery life and thus reduced costs to the user.

Hybrid hearing aids were only produced for about a year before fully transistorized hearing aids took over the market. They are now relatively rare to find.

The first hearing aid using a transistor, the Sonotone Model 1010, reached the market in December 1952. It used two vacuum tubes, plus one transistor in the output stage.

A few other manufacturers quickly followed suit with similar hybrid models. These included:

Acousticon (Models A-300 [1953] &
       A-310 [1953]),
Audiotone (Model 15 [1953]),
Aurex (Model T-2 [1952]),
Bonochord (Transitron M-30 [1954]),
Dahlberg (Model D-5 [1952]),
Danavox (Models 520 [1953] & 537
      [1953]),
Fortiphone (Model 40 [1955?]),
Micronic/Audivox (Model 303-T [Jan, 1953]),
Omnitone (Model T-1 [1954-55]),
Otarion (Models C-15 [1953], C-30
      [1953] & F-22 [1954]),
Siemens (Delta) [1954], and
Telex (Model 954 [Dec. 1952]).

All Transistor Hearing Aids

All-transistor hearing aids first hit the market in January, 1953. The first all-transistor hearing aid was Maico's Model "O", the Transist-Ear. It came out in early January, 1953. (See picture at right.)

Maico's Transist-Ear was followed shortly, either in late January (January 25th is the earliest known ad for this hearing aid) or early February. (On February 4, 1953 this hearing aid was "introduced" by Microtone. (See picture at right.)

The demise of the vacuum tube quickly followed. Most hearing aid manufacturers quickly realized the benefits for both the consumer and the manufacturer.

This remarkable device with its small size, even in comparison with the miniature hearing aid vacuum tubes, and the elimination of one of the batteries in hearing aids allowed much greater reductions in size of hearing aids to follow in the 1950s and 1960s.

This category in the museum includes samples of transistor body aids from 1953 through to the 1980s when ear level hearing aids had become powerful enough to make body aids virtually obsolete except for the most severe hearing losses.

If you want to learn more about the transistor and its use in hearing aids check out:

Bob McGarrah's Virtual Transistor Museum and History Website

and

The CK722 Classic Germanium Transistor Museum