The VTVM (Vacuum Tube Volt Meter) V-7A and V-7AU* came on the market in 1956 and was produced until 1961. It was the successor of the V-7 that was only produced during 1955, that in turn was the successor of the V-6. In 1961 the V-7A was replaced by the IM-11. There is only minor differences between the V-7A and the IM-11 . The VTVM V-1 was one of the first Heathkits that came on the market in 1947, just after the oscilloscope O-1. The circuitry is very similar in all the VTVM's. The V-7 was the first with the components mounted on a printed circuit board.

I have slightly modified my V-7A. I have connected the chassis to mains ground and isolated the negative terminal and the internal framework from the chassis so that floating measurements can be taken. The ¼" connector is replaced with a pilot lamp and the probe resistor is placed inside the VTVM. I have modified my IM-11 and IM-18 in a similar way.

*The Brittish Heathkit factory in Gloucester produced several kits with the letter U added to the designation. Among them was the V-7AU. The U meant The United Kingdom. The V-7AU stayed in production for several more years than the American made V-7A. The V-7AU was still in the Brittish 1969 catalog.  

The schematic of the original unmodified V-7A





The schematic of the modified V-7A




As a new, isolated from the chassis, battery holder I use a plastic film-canister for ordinary film type 135



The battery fit in the film-canister, a plastic bracket mounted and bolt-heads used as battery contacts