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[Amps] Why not to use coax connectors for HV

To: Amps reflector <>
Subject: [Amps] Why not to use coax connectors for HV
From: "Bill, W6WRT" <>
Date: Mon, 24 May 2010 16:05:41 -0700
List-post: <">>
Recently, a couple of members of this reflector suggested using coax
connectors for high voltage. This is a very unsafe idea, especially if
used with actual coax cable, and here's why:

Assuming you have an SO-239 female connector mounted on the power
supply and you either have the HV accidentally turned on or have not
fully discharged the filter caps. When you go to plug in the PL-259
plug you are no doubt holding the metal ring of the PL-259, which
means you are connected to the braid. At the moment the pin contacts
the socket of the SO-249, if there is any current path or leakage from
the coax center conductor to the braid, you are at the full HV
potential. Even without a DC current path, there is still the
capacitance between center conductor and braid, and at high voltage
levels, can deliver a severe shock. 

If you (or some future user of your amplifier) accidentally plugs in
an antenna to the SO-239, the possibilities are even more dangerous.
Many antennas are at the same DC potential between center conductor
and braid because a tramsfprmer-type balun or other matching network
is present, and you can imagine the consequences of a direct DC
connection. Even without a balun, a long length of coax has a very
large capacitance and can easily deliver a lethal shock. 

Even if you are not using actual coax (no braid), do you really want
to be holding on to a metal ring at the moment the plug pin contacts
the HV and there is a possible carbon track or other leakage in the

A properly designed HV connector makes this kind of accident
impossible. Please don't try to save a few bucks by using the wrong
connector for the job. 

Murphy is alive and well, waiting patiently. 

73, Bill W6WRT

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