A pretty cool, very rare piece of test equipment turned up on eBay recently: a 1956 Hycon model 615 AC/DC VTVM. This was a precursor of today’s digital, using analog servo circuitry to drive the numeric digit display.

These were a big-ticket item back in the day:$374.50 in 1956 would have been around $3,200 in today’s dollars, adjusted for inflation!

Cyclometer drive displays started turning up in the 1930s, and disappeared by the 1960s as direct digital read-outs (numitrons and decatrons, nixie tubes, and later VFDs and LED/LCDs) became available. They were initially used in clocks, with cyclometer meters appearing in the 1950s and lasting for about 10 years. Most turned up in even higher-end lab equipment, with cyclometer displays being quite rare on benchtop equipment.

This would be a great collector’s item, especially if you could get it running again! If the servo motor is good, it should be possible; there’s a schematic over at Hycon Model 615: Radiomuseum.

[Vintage 1956 Hycon Model 615 VTVM Vacuum Tube Voltmeter *Non Working*]