Specialists in service and repair industrial electrical installations on will appreciate, I think, a convenient small-sized probe - "kontrolka" 220/380 V.
An indicator here is not "neon", and the thyratron MTH-90. And as the housing is adapted with suitable size transparent (plastic or glass) bottle from under the drugs. Moreover, if the material of such a "body" - glass, to protect its integrity (e.g., dropping) I recommend to wrap the probe in two or three places with electrical tape (in the form of shock-absorbing of the rings). Well, at the styli wear a PVC pipe.
The appearance of small probe-friendlies: 1 - body (black bottle from under the drugs), 2 - damping rings electrical tape, 3 - tube, 4 - flexible wire in the insulation (2 PCs.), 5 - dipstick "0", 6 - probe "phase", 7 - stylus tip (thick tinned copper wire, 2 pieces), 8 - touch plate.
A circuit diagram of the device
The choice of cathode and grid resistors is not too critical and may, accordingly, to be 120 To 150...K and 4 M 10 M...
Collecting probe, make sure it is working. To do this, connect the probe "phase" to the same wire outlet. Then, by touching the touch the plate, make sure that the thyratron is lit. The phase output flag ballpoint handle.
Author: O. Sussen, Mariupol, Donetsk region.