|[AMRadio] You Won't Believe This|
lwill at voicenet.com
Sun Jan 2 09:23:40 EST 2005
But.. To get the correct input power (required in broadcasting) you must
measure plate current not cathode current. Properly insulated meters are
safe and reliable. I agre its either static or magnetic field problem.
At 02:11 AM 1/2/05 -0400, you wrote:
>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.
>Publisher of the Collins Journal
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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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