[Martin Lorton] has a vintage Harmon 4200B selective voltmeter that needed repair. He picked it up on eBay, and he knew it wasn’t working, but it was in good condition, especially for the price. He’s posted four videos about what’s inside and how he’s fixing it. You can see the first installment below.
The 4200B is an RMS voltmeter and is selective because it has a tuned circuit to adjust to a particular frequency. The unit uses discrete components and has an analog meter along with an LCD counter.
