I can recall opening one of these PulseStarter units when I was younger, but didn’t have the skills to fully understand the operation. It’s a lot clearer now, but there is still an oddity of how the thyristor that shunts the starter contacts is kept off if the tube doesn’t strike. My guess is that it turns on just long enough to keep the transistor’s base capacitor topped up, but not long enough to attempt a tube heat and strike.
It’s actually quite a neat circuit. I wonder what sort of thyristor they used before this application specific thyristor was introduced. It would have to have a low gate current like a TIC106M.
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