The Embedded Muse
Since 1997 the Embedded Muse has provided hardware and software tips about building embedded systems.
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Freebies: Eevery month we run a giveaway of something cool. Past giveaways include bench oscilloscopes, USB scopes and logic analyzers, books, development boards, power supplies and much more. Only Embedded Muse subscribers are eligible to win. Enter the contest here.
Given the mention of Heathkit in the January 4 Muse, and the focus on history in both of this month's Muses, this month's giveaway is a circa 1949 VTVM from Heathkit.
What's a VTVM? These used to be ubiquitous in labs but are unknown today. It's a vacuum tube voltmeter. Maybe you have one of those cheap Radio Shack volt-ohmmeters (VOMs). They typically have a terrible input impedance so will load circuits, giving erroneous readings. A VTVM feeds the input to the grid of a vacuum tube ("valve" to our British friends), giving the meter a very high (on the order of 10 MΩ) impedance.
The meter doesn't work. I took it apart and found the power-supply capacitor is bad; probably the others need replacing, too. The selenium rectifier works, but I'd replace it with a silicon diode. This would be a fun repair project. A manual with schematics is here.