[AMRadio] Collins 20V-3 - Happy, Happy

David Knepper cra at floodcity.net
Sun Jan 2 18:40:08 EST 2005

Installed a new 20K/200 watt resistor in the screen circuit to the 4-400A's.
There are two of these resistors in series - I replaced the other one some
time ago.  The problem was none other than an open resistor.  I did see a
whitish power on one end of the resistor which is a sure sign that the
resistor was overheated and open.

What happened when I had no screen voltage on the 4-400A's.  Well, there was
no load on the high voltage power supply which caused the voltage to rise to
over 4,000 volts.  This higher than normal voltage created some kind of
corona effect inside the meter or whatever.  The meter now reads perfectly
once I got the transmitter loaded and with screen voltage applied.

The screen voltage is taken off the high voltage and reduced through two 20K
high wattage resistors.

Now the transmitter performs as it should.

This was a tough problem but could have been easily solved had I checked
these two resistors.  No wonder I was not getting any output.  Pretty
obvious now but not several days ago.

To those who sent me some suggestions via email - thank you.

Dave, W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
Nets:  3805 Khz, Monday/Wednesdays 8 PM EDST
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