Sébastien Bourdeauducq of /tmp/lab and the Milkymist project scored a DIY vacuum tube, and set about testing it out.
I was curious to see how well the PWL triode performed. So I made a little test to measure cathode emission and amplification.
The first step was to build a variable high voltage power supply, since I’m under-equipped enough not to have one laying around. So I used a 20V power supply transformer connected to a 120V variable autotransformer scavenged from a 70′s American-built X-ray machine that happened to have a permanent tap within the first turns, allowing it to step-up the voltage to a nice 180V. For turning it into DC, I simply took the switching power supply PCB from a discarded fax machine, cut it right after the filtering capacitor, and hooked it to the variac. There are easier options, but I did with what I found in my pile of junk :)
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