This Boxy Multimeter Traces Its Lineage Back to a UK Post Office Design in the 1920s

Pseudonymous YouTuber "TheHWcave" has put a multimeter under the figurative microscope to see what makes it tick, but the answer may surprise you — as the device on test was made in the 1960s to a design tweaked from a 1923 original, and yet wouldn't be discontinued until 2008: the AVOmeter Model 8 Mark III.

"The AVO 8 was produced for 57 years, from 1951 to 2008," TheHWcave explains. "The history of this family of multimeters is amazing. From [the] prototype in 1923 to 2008 it had this kind of unique look. The 1930s meter was really more for electrical work. The AVO 7 was targeted at radio engineers and offered a bit more sensitivity, but by the late forties the more advanced electronics of TV sets needed yet another boost in sensitivity — which was the AVO 8."

Named for its ability measure Amps, Volts, and Ohms (AVO), the AVOmeter was a product of the Automatic Coil Winder and Electrical Equipment Co. based on a design by Post Office engineer Donald Macadie. TheHWcave's particular variant, the more sensitive AVOmeter Model 8 Mark III, was built in July 1968, while the line itself would remain in production until 2008 when parts scarcity finally put paid to the range.

As you might expect from a device that traces its lineage all the way back to the early 1920s, the inside of the AVOmeter doesn't look much like a modern multimeter. "This thing is crammed full of components," TheHWcave notes, "which really shows the long heritage and optimizing the placements of everything. If you thought the actual insides of the AVO 8 looked confusing, let me tell you it's pretty much the same with the schematic. I tried to get through it and at least I understand how DC volts and amps work, but I admit the AC part is still a mystery to me."

The full teardown is viewable in the video embedded above and on TheHWcave's YouTube channel.