In article , "Steve Nosko"
writes:

In the 120 vac mode it has a 120 volt cord & plug and an extra wire coming
out (of I believe an octal)
with an alligator clip. You ground the clip and plug it in the way which
has the neon bulb on the rear NOT GLOWING. I believe it must have had a
voltage doubler right off the AC line for the HV, but don't remember the
filament transformer.

When I was young and crazy and using AC/DC home radios for audio amps, I would
rig them with a neon bulb to the chassis, then reverse the AC plug in the
socket if the bulb glowed when I touched the free end. I had only one
"explosion", on a radio that I hadn't install such a neon tester.

Voltage doublers are tricky -- one common circuit ends up with the common
"ground" B- output at a potential different from either side of the incoming
power line. If you build a "hot chassis" radio with it, neither position of
the AC plug is safe.

There is a voltage doubler circuit (2 diodes, 2 caps just like hte other one)
that does indeed preserve the common neutral/ground lead striaght thru, but
ISTR it gives a half-wave rather than full-wave output, so needs more
filtering.
73, Mike K. AA1UK

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