This is a small home-friendly neon bombarder I am using. It allows to properly process neon

tubes up to about 4ft. length with 10mm and short 12mm electrodes without resorting to bring

pole pig transformers and other weird stuff to home :)

First - word of caution. Though small, this bombarder is still capable of generating 270mA

current, which is just in the best range to stop one's heart, and 8kV of open circuit voltage will

do it's best to deliver it! Neon people probably alreandy know it all, but you need to be careful

and obey all rules. Ground this circuit to reliable external ground. Bridge ground to everything

that has a chance to catch high voltage in an event of flashback - transformer cases, metal

manifold parts, gas tanks, vacuum pump etc. Do not touch main stopcock while bombarder is

on! Better do not touch anything. Use red warning lamp and be sure bombarder button do not

stick. Make habit of deactivating main power switch before touching HV alligator clips. Use

quality silicone GTO wires.

Okay. I am using large neon transformers as HV source. I was able to get 8kV/90mA

transformers, slightly large units like 10kV/120mA will work even better. Because of neon

transformers current-limiting nature this circuit is essentially self-regulated and we can spare

using a choke. Current was calibrated to be in best range for 10mm EGL 'throdes and is

regulated in two steps by cutting off one tranformer primary. Disconnecting secondaries is very

unpractical and I found that still connected transformer presents very light load - about 1/10 to

1/20 of open circuit voltage.
Step one shall give about 130-170mA for preheat and step two with all transformers on - about

200-260mA depending on tube lengh. This is enough to process 10mm 'trodes alone. If you

have induction heater you can process much larger electrodes, by using bombarder just for

preheat.

Circuit details:

K1 is 25A contactor, any type suitable for frequent operation.
VDR1-3 are metal oxide varistors. I added them to make transformers life easier by cutting

inductive kickback spikes and to reduce arcing at contactor. They are 20mm 250V AC rated for

220V power. Possibly varistors are not vitally necessary.

All swiches are modular circuit breakers except bombarder button.

It is better to have all tranformers equal. Transformers have to be matched in-phase, by

connecting the same terminals between themselves, or experimentally by getting maximum

voltage.

Neon tranformers have midpoint of secondary winding grounded. That is not best for bombarder application,

making flashback more likely. You may try to disconnect it, but on epoxy-potted transformers

like mine this is impossible. Transformer case shall be grounded anyway!

Credit for this idea goes to Neon John, www.neon-john.net

-Roman