The current, which needs a larger wire, is in the plate/cathode circuits and in the heaters. 24 AWG, I don't know the metric equivalent, should carry all the current that there is in the Crack. Maybe I will drag out an NEC and verify the ampacity of #24.
Edit: Looked, #24 wasn't listed but #27 is good for 1/2 amp, #20 for 5 amps. I think you are safe in the Crack with #24 (nope see PJ's post below) 20 or larger.