Might be best to test only filaments? Even filaments are on different pins than other tubes. Pin #3 and #7 are filament in 4CX250B. They operate on 6.3 volts, couple amps.

You can't test a 4CX250B without a transmitter or special bench setup. Some elements aren't connected to pins. Plate is on the metal portion. Grid #1 is connected to the keyway pin. Cathode is connected to pins #2, 4, 6, 8. Screen is connected to pin 1.

With 2000 volts on the plate it can draw 250 ma. Don't think you want to try this? Since this is a forced air tube can't apply power very long without blowing air over the fins.

Norm

: