ВЭФ 12 (Astrad VEF 12 Project) - including a transistor tutorial

[Nowhere-Man]

I was asked about HT and anode voltage. If HT supply is 200 volts and a valve anode must be 120 volts you need to drop 80 volts (if the original resistor has no marking). If you know the HT current of the valve from the schematic tables, divide this current into the 80 volts you need to drop. This will give you the resistance. So a valve with 5 milliamps 16000 R. I often forget these sums as rarely would I find a missing resistor.