[Amps] testing 572 B tubes

[Peter Chadwick]

If the tubes are soft, there will be (usually) a blue glow between electrodes when drawing current (I have seen it tend more to purple). The emission could be down, which would explain the problem: you could maybe rig up a pulse tester, and pulse the grid positive and measure the plate current. That could be done with a series load resistor 91000 or 1500 ohms at 50 watts, rated for lots of volts!) in place of the RF choke and tank circuit and pulse circuit, and pulse the filament negative by about 70 volts for a 10ms or so. See what the plate current is. All seems a bit messy, though....

73
Peter G3RZP