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The
AC VTVM (Vacuum Tube Volt Meter) AV-2
came
on the market in 1952 and was produced until 1956. It was the successor
of the AV-1 that came
on the market in
1951. In 1957 the AV-2
was replaced by the AV-3. In
1961 the AV-3 was
replaced by the IM-21. In 1968
the IM-21
was replaced by the IM-38. So
far they were all Vacuum
Tube designs and quite look alike, but in 1976 the IM-38 was replaced by the IM-5238
that was an entirely new
modern solid state design. Most other Heathkits
that got the prefix numbers 52
just got a new look and feel, but not in this case. The IM-5238
was produced until 1981.
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