|[AMRadio] You Won't Believe This|
cra at floodcity.net
Sun Jan 2 01:25:05 EST 2005
What is strange about this condition is that the meter deflects correctly
when connected to a multimeter set on ohms.
Positive or red lead to the postive terminal and negative or black lead to
the negative terminal of the meter.
The 4,000 volts when applied, however, causes the meter to deflect
incorrectly. When I tune the transmitter, I can see that the meter pin does
vary but it will not move from the left of zero.
The question that I would have is whether or not anyone else has experienced
this problem, ruling out static electricity on the meter face.
I did remove the meter to clean both the inside and out of the glass but
that did not help.
One day the Collins 20V-3 worked perfectly and the next day, as they say,
the plate current meter went "nuts."
By the way, the R.F. ampere meter is acting strange as well. The needle
quivers as if it is charged with static electricity.
Could it be that the meter panel which is insulated phenolic needs to be
discharged somehow. I am lost at this point.
I am inclined to believe - as so many of you suggested - that the meter or
meters have contracted static electricity.
Thanks to all who have replied.
Back to the drawing board as they say.
Publisher of the Collins Journal
Secretary to the Collins Radio Association
Nets: 3805 Khz, Monday/Wednesdays 8 PM EDST
14250 Khz Saturday, 12 Noon EDST
----- Original Message -----
From: "David Knepper" <cra at floodcity.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Sunday, January 02, 2005 2:11 AM
Subject: Re: [AMRadio] You Won't Believe This
> John, thank you for this.
> Collins engineers did not adhere to safe operating practice when they
> 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.
> Dave, W3ST
> Publisher of the Collins Journal
> Secretary to the Collins Radio Association
> Nets: 3805 Khz, Monday/Wednesdays 8 PM EDST
> 14250 Khz Saturday, 12 Noon EDST
> ----- 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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