Did you read disclaimer ? Then let’s go.
Neon bulb is hard to find. Why not replacing it with a long lasting LED ? Supply for the light was measured at about 110V AC, with EHT powered at 220V AC. Thus, as you can guess, this comes from an output of the transformer.
There are a great deal of tutorials on how to connect a LED to high voltage AC. Here I will use a resistor 1W 22kOhm (that supports high voltage, contrary to 1/4W, and dissipates up to … 1W), a diode EM516 (a bit overkill but small form factor and supports HV), another resistor 1/4W 100kOhm (low voltage is not an issue for that one, the smaller size the better).
22kOhm, LED, diode are in serial (take care to polarity of diodes). 100kOhm is in parallel with LED. All this fits nicely inside existing package, as you can see on pictures.
This makes a peak current of 110*sqrt(2)/22e3 = 7mA. LED is claimed to support up to 20mA. And 110^2/22e3 / 2 = 0.275W in main resistor which is far below 1W (but 1W is nevertheless required for high voltage). Note the “/ 2” which comes from the fact that the LED passes only half of the time. HV diode + 100kOhm are there only to handle high reverse voltage, avoiding LED to support it.
If you don’t care about keeping original design, easiest solution is probably to get this reference if you can find it: Arcolectric C0430 R 28.6*14.1mm 110V Red. It should easily fit into existing hole 30*15mm.
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