[AMRadio] You Won't Believe This


David Knepper cra at floodcity.net
Sat Jan 1 18:30:36 EST 2005


I own a Collins 20V-3 broadcast transmitter that is at the Collins Radio
Center.

The transmitter has been restored and worked perfectly after modifying it to
160 meters.

Now, the plate current meter (0-800 ma.) is reading to the left of "0" with
only the high voltage lead from the smoothing choke attached!!

The high voltage meter is showing 4000 volts.  The positive post of this
meter goes to the positive post of the plate current meter through some
multiplier resistors.

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.

Disassembled the meter to see if it may have a carbon path through the case
to ground.  Nothing.  The meter looks "normal."

When I hook a multimeter to the terminals:  red to positive post and black
lead to negative post on the meter, the needle deflects upward, which is
normal for a current meter.

I am really stumped on this problem.

If someone told me that a current meter could deflect left of zero with only
one lead attached, I would have thought that this was some kind of psychic
phenonomen.

Could the meter have changed polarity?

Can anyone tell me what is going on.


Thanks
Dave, W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
www.collinsra.com
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