Vintage Heathkit IM-104 Solid-State Voltmeter
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This vintage Heathkit IM-104 Solid-State Voltmeter kit showed up on eBay. Although I only own a couple Heathkit items, I have been saving the images of many unbuilt kits in order to preserve the history. They regularly appear and disappear on eBay all the time - some models more than others.

One of the earliest instances of the IM-104 Solid-State Voltmeter being offered for sale was in the Spring 1976 Heathkit catalog (p54), at a cost of $94.95 ($504.55 in 2023 money per the BLS) in kit format, or $149.00 full built and tested. That was/is a lot of cash to lay down for a multimeter that measures AC/DC voltage and current, and resistance. However, the alternative if you needed a high input impedance instrument, this was still cheaper than buying a vacuum tube voltmeter (VTVM), and it is much smaller, lighter weight, and portable due to being powered by batteries (a D cell and four AA cells). An article like "The Case for the Transistorized Multimeter" was evidently deemed necessary in the 1968 issue of Popular Electronics magazine to convince the VTVM faithful that the newfangled DMM would make their lives better.

From the Spring 1976 Heathkit Catalog:

Heathkit FET taut-band VOM - ten megohm input in a portable meter.

A portable lab-grade FET VOM combining accuracy, versatility, convenience and ruggedness - in an easy-to-build dollar-saving kit! Our IM-104 has low-drift 1% precision metal film and wirewound resistors for exceptional stability. Nine DCV & ACV ranges measure from 0.01V to 1000V. Six current ranges cover 0.001 mA to 1000mA, DC & AC. Seven resistance ranges from 1 ohm to 100 megohms, conventional or low voltage modes. Decibel ranges from -40 dB to +62 dB. DC null scale with better than 1 mV resolution. The 4 1/2" ruggedized, taut-band meter is diode protected, built to take plenty of abuse. Built-in circuitry shows battery condition at the flip of the range selector. Three evenings put this great portable VOM on your bench.

Kit IM-104, Shpg. wt. 4 lbs. 94.95

Assembled SM-666, has additional 1μA current range, less 100 & 1000 mA ranges, Shpg. wt. 4 lbs. 149.00

IM-104 SPECIFICATIONS

DC VOLTMETER - 9 ranges: 0.1, 0.3, 1, 3, 10, 30, 100, 300, 1000V. Input resistance: 10 megohm. Accuracy: ±2% of full scale (meter in horizontal position). AC rejection: Accuracy not affected by impressed 60 Hz sine wave with rms 2x greater than full-scale value.

Heathkit products were well known for the completeness of its instruction manuals, with clearly illustrated instructions. During the writing and editing process, Heathkit employees were given pre-production kits to take home and build, while annotating any difficulties or errors encountered. Doing so helped minimize the situation where the writer inadvertently assumes his own familiarity with the process is shared by the customer. Having built a few Heathkit products myself in the 1970s when I did not have a lot of experience with electronics assembly, I can attest to the user friendliness of the instructions. Heathkit still sells many of its vintage manuals for around $15, which is what you would pay on eBay.

Contact Info

Heath Company (Heathkit)
Operations: PO Box 15, Ottsville, PA 18942
R&D/Mfg: PO Box 3115, Santa Cruz CA 95063
Phone: +1 (831) 480-4368
E-Mail: info.2015@2015.heath.company

Posted November 29, 2023