The DVM has a 3.5-digit display consisting of:
This DVM is a bit large. The circuitry is distributed over 9 circuit boards with a quite spacious design style. Eight circuit boards connect to a bus board that doubles as power supply board. All the boards are placed in a card cage that hinges out for easy service. The input attenuators and range switches are contained within a screening box. This DVM has a remarkably small power transformer. It is easy to guess why: the discrete logic circuits use much less power than TTL circuits. And the run on a low clock frequency, as low as 160 kHz.
This DVM contains a lot of transistors, even though the circuits are designed reasonable efficiently. Some of the types used:
I bought this digital voltmeter through an Internet auction site in 2012. When I collected it, the man who sold it told me it dates from 1965. The production codes on the semiconductors and nixies seem to hint at 1965 indeed, making this meter the oldest digital instrument that I have. It does seem to work, but I wasn't yet able to test its accuracy. Before I do that I must replace the rubber mains cord, that is all but falling apart.
Copyright © 2012 by Onno's E-page published 2012-06-18, last updated 2013-10-06