Zerad Model 122 Universal Double-Scale Hearing Aid Battery Tester
The Zerad Model 122 universal double-scale hearing aid battery tester
was made by/for the Zenith Radio Corporation, Hearing Aid Division of
Chicago, IL to test the A and B batteries common in hearing aids during
the 1940s. Since the "B" scale reads to 45 volts, it indicates this
battery tester came out in the early 1940s.
Incidentally, the name "Zerad" is a contraction of the name Zenith
Radio Corporation ("ZE"nith "RAD"io), the makers of the very popular
Zenith hearing aids of the day.
There were a number of battery meters that looked similar except for
the company name on them. It appears one battery meter company designed
the original meter and then manufactured and branded it for the various
hearing aid companies that wanted one.
Normally (by convention) you touched the one tip of the probe to the
positive terminal of the battery, and touched the "foot" (7-o'clock
position) or the "knob" (12 o'clock position) to the negative terminal
of the battery.
Notice that the probe tips are labeled "A" and "B"
and are painted black and red to match the meter scale. When you were
testing an "A" battery, you used the "A" tip which was connected to the
2 volt range. Similarly, to test a "B" battery you used the "B" tip
which was connected to the 50-volt range.
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