This was just for fun, not a serious project. As per info online, it’s supposedly from the 1945-49 era. Fortunately for me, someone donated it and the only part that I was interested in was the fact that there is no schematic available online. And no surprises here, the condition was also not that good.
This is how I received it.
And this is after restoration –
So I here is the flow of events in a video, including the side by side performance along with HP/Agilent 34401A 6.5 Digit Meter 😉
Video #1 – Heathkit V2A – Repair/Restore
Also, I traced the schematic and attaching it here.
Heathkit V2A Vacuum Tube Volt Meter (VTVM) Schematic
This is a 4A schematic I updated to reflect the changes for 2A. There are no major changes, other than a few missing resistors, changes in resistance values, and a missing AC Balance Pot.
One major change is the use of 6X5 as rectifier, instead of semiconductor in 4A. I have identified the changes above in RED.
8.3 Ohm Resistor in the battery circuit was bad, I used a 47 Ohm and 10 Ohm in parallel to arrive exactly 8.3 Ohm. I had to try few 47 Ohm resistors until I could get exactly 8.3 Ohms to get the right value within tolerance window.
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Lazy Electrons 