I found a thyratron tube at a yard sale recently and I want to build a circuit to heat the filament and illuminate the mercury vapor for purposes of building a novelty lamp. The filament is just 2.5VDC at 7 amps and I have a transformer for that. To light the vapor I will apply DC rectified and smoothed from the AC mains. The illumination is related to current, and to achieve maximum illumination of the electrode I want to achieve something on the order of milliamps, above the current for Townsend discharge but below that of arc discharge. I don't know what those values will be so let's say, between .01 and .5 amps. So V = IR 120 = 0.01R 12000 Ohm = R1 120 = .5R 2400 Ohm = R2 So my load resistor in series with the thyratron will be a 10K rheostat in series with a 2.4k Ohm resistor. Hoping for any input from someone with tube experience, if this might work.