[AMRadio] You Won't Believe This

John Coleman, ARS WA5BXO wa5bxo at pctechref.com
Sat Jan 1 23:31:07 EST 2005

I gather from the text about the HV meter and current meter that the
current meter is above ground by 4000 Volts.  I know that there are a
lot of special mounting devices and hardware for this purpose but I
still feel that it is a bad idea.  I have always made sure that HV
current metering was done in the current path that is close to ground
potential.  As a further precaution it is a good idea to put a 50 Volt
or less avalanche diode across the meter in case it should become open.
As for the defection phenomenon, it might even be possible that the
continued HV on the meter has put permanent static charge in the
molecular structure of the plastic.  If this is the case then any
connection even a ground on the meter would cause a deflection.  In any
case I would move the current metering circuit to the cathode circuit or
the negative return of the power supply.  Modification of initial
circuitry sometimes requires lifting all the ground connections of
filters and/or chokes to get a floating ground and then passing that
through the meter for current readings.  I my opinion it is well worth
the effort.  I always put chokes in the negative lead of power supplies
as well.  

It is an interesting phenomenon though. So please let us know what you
do find as the cause.

73, John, WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of David Knepper
Sent: Saturday, January 01, 2005 5:31 PM
To: Discussion of AM Radio; Collins Mail List

Subject: [AMRadio] You Won't Believe This

That is right, only one lead connected and the meter is reading negative
current.  I switched this lead to the negative post and the meter still
deflects downward past zero.

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