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 However, for most individuals, never having been exposed to out-of-date hearing aids, there is little reason to expect to know what some of the sizes and types were.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.
A following post will show how some of these batteries actually fit inside the hearing aids.