|[AMRadio] You Won't Believe This|
cra at floodcity.net
Sun Jan 2 01:11:25 EST 2005
John, thank you for this.
Collins engineers did not adhere to safe operating practice when they placed
the 800 ma meter in the positive lead going to the R.F. choke. It should
have been in the negative lead as you suggested.
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----- Original Message -----
From: "John Coleman, ARS WA5BXO" <wa5bxo at pctechref.com>
To: "'Discussion of AM Radio'" <amradio at mailman.qth.net>
Sent: Sunday, January 02, 2005 12:31 AM
Subject: RE: [AMRadio] You Won't Believe This
> 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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