Heath Heathkit IM-28 VTVM Vacuum Tube Voltmeter
These meters were popular because of their high input impedance and ability to check solid state circuits accurately without excessive loading, as would occur with the cheaper VOMs of that era. Even today, these analog meters are handy for situations where the option for a “center zero” is desired, or when adjusting circuits where a “dip” or “peak” reading is required.
IMPEDANCE: 1M with 40uuf shunt at input terminals
FUNCTIONS: AC Volts, DC- Volts, DC+ Volts & Ohms
AC/DC RANGES: 1.5, 5, 15, 50, 150, 500, 1500
OHMS RANGES: x1, x10, x100, x1000, x10K, x100K, x1M
BATTERY: Size C (for ohmmeter use)
AC POWER: 105 - 125 VAC (50/60 Hz) 10 Watts
(Can also be wired for 210 - 250 VAC)
OVERALL SIZE: 5” H x 12-11/16” W x 4-3/4” D
The meter was tested before listing by comparing to a Fluke DVM at 30 VAC and 6 VDC for voltages, and at 100 ohms and 12 K ohms for resistances; readings looked comparable. Since the manual has complete calibration instructions, you can tune it up any time you like!
The heavy-duty mounting bracket can be used for either table-top use or wall mounting; the wall mounting is nice as you can keep the meter up off your workbench where it is out of the way and convenient to see.
This VTVM was assembled in the mid 1970s and is in excellent condition other than a crack in the meter cover that starts in the upper left corner and extends about 2" inward; the crack does not impact the meter's operation. This is a nice vintage meter; see the photos and judge for yourself.
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