Heathkit IM-17 Utility Solid-State Voltmeter

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Sometime around late 1977, a year or so prior to reporting to Lackland Air Force Base for Basic Military Training (BMT) with plans to pursue a career in electronics, I began boning up on my admittedly lacking electronics skills. Having spent the past few years as an electrician, including a couple years in vocational school, I was familiar enough with the big stuff that could easily kill me, but I didn't know much about about electronics with its small components and low voltages. To assist me with my goal, I purchased a couple Heathkit kits and carefully studied all the information provided, then proceeded to assemble and test everything. My first project was this IM−17 Utility Solid-State Voltmeter. It was simple enough for even me to be successful. Although it was called a voltmeter (AC and DC capability), it also measured resistance, so technically it was a volt-ohmmeter. I'm not sure why the designers didn't add a current measuring function. A few years later, Heathkit added a transistor checking circuit and re-designated the the IM−5217 (see the 1982 Heathkit Christmas catalog page).

Heathkit IM−17 innards. Note the 9 V transistor radio battery in the 8.4 V mercury battery holder.

Heathkit IM−17 panel and printed circuit board assemblies.

Heathkit IM−17 bare plastic case

Heathkit IM−17 kit contents.

Recently, I did some minor cleaning and calibration of the old IM−17, and it still works perfectly. The manual suggests using a 1.5 volt dry cell battery for the DC calibration and the 120 volt wall socket for the AC calibration, if no better sources exist. A kit-built 10 MHz bandwidth oscilloscope I assembled many moons ago specified the same two types of calibration sources. Fortunately, I had sources a little better than a battery and a wall socket, and unlike the earlier exercises, I now have a good quality digital multimeter to verify the voltage levels (and better sources). The IM−17 is a strange beast in that the AC and resistance measurements are made using the red and black leads, and the DC measurement is made using the black and gray leads. The gray lead is shielded. An auxiliary jack is provided for using a Heathkit high voltage probe or a Heathkit RF voltage probe (neither of which I own).

Also, the IM−17 originally used a 1.5 V carbon C-cell and an 8.4 V mercury cell (no longer manufactured due to hazard reasons), but now a standard 9 V transistor battery is being used successfully in place of the 8.4 V cell. The manual specifies that a 9 V battery can be substituted, but the lifetime will be shorter and the meter "zero drift" could be greater.

The entire Assembly Manual has been scanned and posted below. Heathkit spared no time or expense creating their manuals. Very clear instructions and expertly done illustrations make assembly nearly foolproof. Detailed calibration and usage instructions are provided, as well as a circuit description. According to a 1972 edition of Mac's Service Shop entitled, "Philosophy of a Kit Manufacturer," their product development process at Heathkit involved having some employees build the kits exactly per instructions, and then revisions were made to the documentation as needed prior to making them available for sale.