Heathkit IM-13

A six-inch, 200-microamp meter movement, a gimbal bracket that tilts to any angle, and a price that undercut the competition — the shop-bench VTVM that taught a generation of technicians how to measure.

Overview

The IM-13 is a vacuum tube voltmeter, sold by Heathkit in both kit and factory-assembled form. The idea behind it is simple: put a big, readable meter where the technician can see it. The meter is a 6-inch, 200-microamp movement with multicolored scales. The cabinet hangs from a gimbal bracket with two thumbwheel nuts on the sides, so the meter tilts to any angle and mounts under a shelf, on a wall, or anywhere around the bench. That puts it at eye level and tilted toward you, instead of flat on a crowded work surface.

The measurement set is the classic VTVM menu: AC volts (RMS), DC volts, resistance, and db. There are seven ranges, with dedicated low-voltage AC scales at 1.5 and 5 volts. The IM-13's own documentation flags these separate scales as a high-accuracy feature, and they help when you're chasing a fraction of a volt in a preamp stage. Ohm-meter work is covered by multiplier ranges. The unit uses a single AC/Ohms/DC test probe with a switch, plus one input jack serving both the probe and the ground lead. Flip the switch and you're measuring AC/ohms or DC without re-patching, which saves you a tangle of test leads.

Heathkit's own catalog copy says the IM-13 shares the high-performance specifications of the IM-11. The additions are the 6-inch meter, the extra low-voltage AC scales, the gimbal mounting bracket, and "service bench" styling. The IM-11 is the smaller, plainer sibling in that comparison. Calibration and zero/ohms adjust controls sit on the front panel, so routine calibration checks don't require pulling the case. That's handy on an instrument that will drift and need touching up over years of service.

The IM-13 uses conventional wiring in a deliberately roomy layout, which Heathkit pitched as both a fast, easy assembly and a serviceability virtue. It's built with 1% precision resistors throughout, and the documentation promises "years of fine service" from the component selection. The kit version weighs 7 lbs. The factory-built IMW-13 is listed at 8 lbs in one catalog entry and 7 lbs in another, a minor catalog inconsistency, but the assembled unit is essentially the same chassis. It's ready to work as soon as the internal ohms-scale battery is installed and the gimbal bracket is mounted.

The kit listed at $32.95, and the factory-assembled IMW-13 at $49.95, both sold on Heathkit's no-money-down, $5-a-month terms. An export model was available for 115/230 VAC at 50-60 Hz, with prices on request. Heathkit also sold the IM-13 bundled with the EF-1 course kit, "How To Understand And Use Your Vacuum Tube Voltmeter," as the EF-1-4 combination at $39.95, saving a few dollars over buying separately. The EF-1 itself, a text plus special power supply for VTVM owners, ran $8.95 alone. The course was pitched as applying to all VTVMs, not just Heathkit's.

The period press took notice of the price. DB-Magazine (February 1968, p.27) ran Heath under the banner "Best Value Meters," part of the magazine's ongoing coverage of the kit maker's test gear. That's advertising-adjacent placement rather than a lab measurement, but it tracks with how the IM-13 was positioned: not the most precise instrument on the bench, but a lot of meter for the money. The Audio (October 1964, p.117) issue of the same era carried Heathkit's "KIT or ASSEMBLED!" tagline in its pages, the two-format pitch the company used on everything from VTVMs to tuners.

An owner today needs patience with tubes and calibration. It's a VTVM, so the zero and ohms adjustments need attention. The front-panel access to calibration controls is there because that's routine maintenance, not a repair. The 1% resistors and the conventional wiring make the unit straightforward to work on, with no dense PCB to desolder and no proprietary modules. The 200-microamp movement is the part that matters most. A bent needle or a sticky pivot is the failure to worry about, and everything else is replaceable around it.

Collectors and bench techs tend to treat the IM-13 as a working instrument rather than a display piece. It's a VTVM from the era when VTVMs were the standard front end for service work, and its meter is readable from across the room. The gimbal bracket, the separate 1.5 and 5 volt AC scales, and the single switched probe are the details that separate it from the IM-11, which it shares its specs with.