VTVM 1/4" plugs..

[Emil Dular]

This exchange got me curious, so I dug out my Heath 336 high voltage probe
instruction sheet, dated 24 Jun 1966.  Just as Paul observed, the old single
pin Amphenol mic conector (Heath P/N 432-1) and common Switchcraft phone
plug (Heath P/N 438-3)  are used, as was common back in the day of tube
TV's.

The sheet clearly states: "Caution never use the probe on DC voltages above
30,000 volts. While the conductors inside the handle and the test lead never
carry more than 300 volts when the probe is properly connected, THESE PARTS
WILL BE EXPOSED TO THE FULL 30,000 VOLTS, IF NOT CONNECTED TO THE VTVM."

Pretty clearly, the standard phone plug is good for ranges most VTVM's of
that era would see, 500 volts was pretty common with a 1000 volts on a nicer
unit.

Emil WD4SCZ

> I just put 1560 VDC on a typical phone plug.  It is even a stereo plug.
> All sections tested.  It didn't show any leakage or signs of arcing over.
>
> I won't say the test is all conclusive.  Just thought I'd give it a test.
> Bob W5UQ
>
>
> Kent Kressenberg wrote:
> > PJ-055B plugs are often still available... keep an eye on ebay.
> > bought a lot of TWELVE (12) of them a few months ago...
> >
> > 73 de WB4SYU,
> >
> > Kent
> >
> >
> >
> >> If you can find some military surplus headsets (oldies) they usually
> >> have a
> >> PJ-055B plug. These have a much wider insulating band between the tip
> >> and the
> >> sleeve. I have a couple here with a 3mm insulation ring, one of the
> >> Heath plugs
> >> has a 2mm insulation. All my "standard" plugs appear to be about 1mm,
> >> depending
> >> on where they were made. I have even thinner insulation rings in my
> >> parts bin for
> >> guitar cables (OK for audio).
> >>
> >> Up to the recent exchanges of notes on these I had never really paid
> >> much
> >> attention to the insulation rings.
> >>
> >> Cheers
> >>
> >>
> >> Keith Harvey VA3KRV


The 1/4" phone plug and the familiar mono screw on mic connector were
> the common choice for probe attachment back in the radio tv repair day.
> My observations, FWIW. Hope it helps.
> Paul K0UYA

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