[userbinator]

Surprisingly, despite being exposed to 600 volt pulses, the problem with this 28 volt bulb wasn't that it had burnt out, but that one of its tiny leads had broken.

That's because the bulb doesn't have 600V across it. In a normal application as an actual glowing bulb, it's rated to have 28V across it, pass a certain current, and emit light at a certain brightness.

In this application, it's being used as a current limiter, and the high voltage supply to CRT grids is very low current (several milliamps at most) --- thus, the current through the bulb and the voltage across it will also be very low.

[tyingq]

It would have 600v if whatever else it was in series with shorted. It's not clear how much resistance the rest of the circuit has, so it's hard to say whether the pulses briefly exceed 28v across the bulb or not.

It's not uncommon to exceed forward constant max current specs for an LED with pulses (PWM), for example.