Vintage Hearing Aid Batteries
Wayne Staab, PhD (and official Canadian Audiologist Audiology Historian) and Robert Traynor, PhD will alternate Stories from our Past which are about technical innovations and approaches that are now ubiquitous in our field or were important in the development of our field. In many cases, these stories will be written by the innovators themselves.
Reprinted with permission from HearingHealthMatters.org
In researching vintage hearing aid batteries, occasional references are made to the power supplies (batteries) used. However, for most individuals, never having been exposed to out-of-date hearing aids, there is little reason to expect to know what some of the sizes and types were.
This post will review some of the commonly-used batteries and cells at the time, but which are not generally found today. This is a continuation of an historical overview of hearing aids in the earlier vacuum tube era. Considerable text explains the early hearing aids, but not much is available identifying the power supplies used. That is one purpose of this post.
Much credit for the development of smaller hearing aids that could be head-worn, has been attributed to the development of the transistor, over vacuum tubes, which required only a single battery and lower voltage. However, battery companies were always looking to reduce the size and efficiency of their products, including those for hearing aids.
Companies that produced batteries for hearing aids in the early 1950s were National Carbon Co. (Union Carbide), P.R. Mallory and Co., Ray-O-Vac Co., General Dry Batteries, and Burgess Battery Co. To the best of my knowledge, there are only three major companies remaining that manufacture hearing aid batteries.
Vacuum Tube Hearing Aid Batteries
Vacuum tube hearing aids required two batteries, a 1.5 volt “A” battery that powered the vacuum tube filaments, and a higher voltage “B” battery to power the plate circuit to amplify the sound. A few very early “A” batteries were reported to be 3 volts, but the most common, and that which was last used for vacuum tube hearing aids was 1.5 volts (not the 1.4 volt batteries that many are familiar with and which were used with transistor hearing aids). Some very early vacuum tube hearing aids used “B” batteries as high as 90 volts. “A” batteries were used at a rate of approximately 2 or 3 times greater than “B” batteries.
Early vacuum tube hearing aids consisted of a two-pack (or multi-pack) arrangement; one pack for the hearing aid (microphone and amplifier), and the other for the two batteries.
Technology that permitted making better and smaller vacuum tubes led to size and power reduction. This size reduction led to the monopac body-worn hearing aids, where the microphone, amplifier, and power supply were all housed within the same hearing aid case (Figure 1).
The reduction in vacuum tube size permitted a similar reduction in battery voltage needs, therefore leading to smaller battery sizes. As an example, the first vacuum tube hearing aids mostly required at least 45 volts for the “B” battery. This later dropped to 30 volts, to 22.5 volts, and then to 15 volts. Examples of some of the earlier “B” batteries, along with their identification and voltage are shown in Figure 2. Once the transistor came into use, and/or when mercury replaced carbon-zinc as the active ingredient in batteries, button-type cells began to emerge. Unlike today, during the 1940s, 1950s, and even into the 1960s, hearing aid companies often had special sizes and shapes for batteries used in their products. In reviewing hearing aid batteries during that time period, at least 60 different battery sizes and shapes were used. Although some were interchangeable, many were not.
The “A” battery saw changes in its size as well, as shown in Figure 3. These changes consisted primarily in size reduction, with essentially all being of 1.5 volts. Both the button-cell type on the right and those on the left were used during the same time frame. Just as with “B” batteries, a number of different designations existed for the “A” battery. Just a few of these included: 1035, Z-1PL, RM-4, RM-3, RM-1, Z-225, RG-1, RG-3, 1015E, 1016E, M10H, No. Z, Z-1M, M-910H. The size and shape of the “A” battery was often determined by the design configuration of the hearing aid.
Only partial transition occurred from taking the “A” battery from paper-wrapped to metal-cased button cells. Figure 4 shows the major “A” battery button cells that were used in vacuum tube hearing aids. Those shown were manufactured by P.R. Mallory Co. of North Tarrytown, NY. They produced the Mallory RM-4, Mallory RM-3, and the Mallory RM-1. All three are 1.5 volts. These were used in vacuum tube hearing aids in the late 1940s and early 1950s. Following the introduction of transistor hearing aids, the RM-1 was sometimes used as the power supply for the hearing aid.
Button batteries (cells) came into extensive use with the introduction of mercury as an active ingredient in hearing aid batteries. They started with the “A” batteries introduced by Mallory, but transitioned to the single power source following the wide use of transistors in hearing aids. Shapes and designations of just some of these are shown in Figure 5. In some cases, button batteries were stacked, or doubled up into a single package, as shown in Figure 6. That package consists of two RG-1 (RM-1) batteries soldered together and covered with paper to represent a single battery. Some hearing aids just put two of these back-to-back in the same battery compartment slot.
Batteries for Early Transistor Hearing Aids
The previous section was about early vacuum tube and transistor hearing aids, and the hearing aid batteries they used. A tremendous change occurred in hearing aid size in going from vacuum tubes to transistors as amplifiers. Much of that related to changes in the battery size as well, as previously discussed.
This post is intended to show how some of these batteries actually looked as attached and/or inserted into hearing aids, and how these changes occurred over time, especially during the late 1940s and into the 1950s.
Battery Supply for Vacuum Tube Hearing Aids (1942 Product)
These are generally the images shown in any discussion about the history of hearing aids. This post will not overdo this, but instead show how these power supplies operated with one of the author’s old boxed-up hearing aid collection units.
The Zenith A2A was an early two-part hearing aid (Figure 7). Part one consisted of the hearing aid, and part two consisted of the two large batteries required to operate the hearing aid. The batteries were often contained in the same pack (pack shown in the right image in Figure 1 and shown in intended use in Figure 8.
Battery Supply for Vacuum Tube Hearing Aids (1946 Product)
By 1946, both the vacuum tubes and batteries had been reduced in size, as shown in Figure 9 and were housed in the same package (minus the receiver). This included both the “A” and “B” batteries.
Beltone Harmony (1946)
The Beltone Harmony hearing aid shown in Figure 9 is such a monopac. This vacuum tube hearing aid contained a RM-4 “A” battery and an Eveready 413E “B” battery in the same case as the remainder of the electronics.
Battery Supply for Vacuum Tube Hearing Aids (1947 Product)
By 1947, body-worn hearing aids had made continued improvements in vacuum tube size and lower battery power requirements.
Acousticon A 90M (1947)
Figure 10 shows the Acousticon A 90M body-worn hearing aid. This hearing aid still used the 1.5-volt RM-4 “A” battery, but the “B” battery voltage had dropped to 15 volts. This hearing aid was slightly smaller in size than the Beltone Harmony of just one year earlier, showing that even small changes in size was a design goal.
Battery Supply for Vacuum Tube Hearing Aids (1950 Product)
Microtone T-10 or Microtone “Ten” (1950)
This was a rechargeable hearing aid using 3 vacuum tubes. It was powered by a RM-1 “A” battery and a 504 “B” battery (Figure 11). It was identified also as “Sealed Power.” This hearing aid had a Sterling Silver case and came with a dresser top storage case that had a battery tester called the “Micro-Mizer.”
Battery Supply for Vacuum Tube Hearing Aids (1951 Product)
Continued size reduction, but with increased power was a design feature in the early 1950s.
Zenith Super Royal (1951)
A good example is the Zenith Super Royal in 1951 (Figure 12). This was one of the last vacuum tube hearing aids (3 vacuum tubes) made by Zenith, changing to transistorized hearing aids in 1953. This unit was unique in that it used four batteries: two 1.5 volt “A” batteries (Zenith size 222, same size as RM-1), and two 15-volt “B” batteries. Only one of the “A” batteries was in use at any given time, with the user periodically switching between the two “A” batteries (switch on the top of the aid – A1-A2) to provide some recovery while the other was being used. The “B” batteries (22.5 V) were connected in series to produce 45 volts for increased output power.
Batteries from Early Transistor Hearing Aids
The transition from vacuum tube to transistor hearing aids occurred in the mid 1950s. The transistor allowed for a single power supply, and voltage as low as 1.4.
Being able to operate on 1.4 volts reduced tremendously the power requirements, both in size and required voltage from that required for vacuum tube hearing aids. Essentially all hearing aids made this transition during this period. Two, from the same company, that served as examples of how a smaller- sized power supply was used were the Zenith Model 75-X and the Zenith Regent (Figure 1). Both used a 1.4 volt 401 battery; the Model 75-X using a single battery, and the Model Regent using two 401 batteries.
Zenith 75-X (1954)
The Zenith “75-X” used a Zenith “N” size 1.4 volt. This was Zenith’s label for the 401 battery. The hearing aid was a 3-transistor amplifier housed in a chrome case (some say polished aluminum). It measured 65 x 45 x 18 mm. It used a single 401 battery. The hearing aid was manufactured by what was then a Division of Zenith Radio Corporation, Zenith Hearing Aid Division. The reason for the model number was that the recommended cost to the consumer by Zenith was $75 – something not looked upon favorably by those selling the product.
Zenith Regent (1955)
The Zenith “Regent” transistor hearing aid was a 5-transistor aid of a push-pull (PP) amplifier type. It measured 81 x 45 x 17 mm in size, and consumer cost was designated at $195. This unit used two 401 batteries (Figure 13).
Sonotone 200 Transistor Body-Worn Hearing Aid (1956)
The Sonotone 200 was a 4-transistor push-pull hearing aid. It measured 76 x 45 x 16 mm in size (Figure 14). The hearing aid had discrete-position sliding switches, shown above the battery. The left control is a 4-position power control. The center control is a 2-position low-pass filter. The right control is a 2-position high-pass filter. The battery was a Sonotone 600 battery of 2.8 volts. This was essentially two 401 batteries in the same plastic housing, soldered together in series. This can be visualized better in Figure 15.
This post completes the series on vintage hearing aids and batteries found in the author’s garage in an old box. What was reported in this series did not attempt to provide a detailed history of development, but to highlight some of the unique features of hearing aids found in that box. In this way, the intent was to help preserve part of the history of hearing aids, especially of those in the late 1940s and through the mid 1950’s.
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