Advance DVM1

This British DVM is really well built. It comes in a nicely serviceable case ful of circuit boards. This meter has eight ranges:

• 2, 20, 200 and 2000V DC V
• 2, 20, 200 and 1000V AC V

There is a second switch to choose between DC and AC ranges. The same switch is used to select a number of callibration screws, the functions of which are unclear without the manual.

The DVM has a 3.5-digit display consisting of:

• A Hivac XN6 displaying digit “1” and + and - sign.
• Three Hivac XN3 numerical nixies.
• Separate neon bulbs for decimal points.

Every nixie tube has its own circuit board with a ring counter and driver transistors. All the logic circuits are using discrete components, no IC's in sight.

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:

• GET889 (Mullard) in numbers, for digital circuits,
• 2N1302 (RCA) for digital circuits,
• A1670-1 (SGS) as nixie drivers,
• 2S512 (Texas Instruments) for analogue functions,
• 2S703 (Texas Instruments) for analogue functions,
• BCY33 (Mullard?) for analogue and digital functions,
• 2N3053 (RCA) in the power supply,
• and a lot of diodes for gates.

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.