HELP!! Valiant doing sneaky things!!

[Brian Carling]

Hi guys! Any chance of your using a little expertise to help here?

I am stuck with an annoying problem in my Valiant and had to shut
down CX operation until I can figure it out!

I hear a POP! sound about every 10-15 seconds when the rig is
thrown into TRANSMIT, and the plate current will increase and then
slowly climb back down to quiescent current of 10 mA unkeyed.

Plat ecurrent will surge to about 400-500 mA and then quickly drop
back to normal 10 mA!

It will also happen when I am transmitting AM or CW. A POP occurs and
the plate current (and power out) will kinda surge to a high level
and then drop back. Happens more and more often now.

It used to happen every 30-40 seconds. Now it's about every 10-20
seconds. I am afriad that a transformer or choke might be arcing
internally. I hav ereplaced all of the HV ELctrolytics recently and
that did not help or change anything.

I can't figure out WHAT is popping!
It sounds like an ARC but I can't see where!

The voltage on the hot end of  R16 remains pretty constant. 790V DC
but on the other end and it is normally 140 VDC (clamping voltage,
but will JUMP up to 280V DC when I hear the pop.

Then it will slowly drain back down to 140V over about 1-2 seconds.

Darn, I wish I could figure this out and get back on CX!!

The RF Bias remains constant at -52V DC

NOW, if I adjust the CLAMPER so that it is all the way clockwise,
I STILL hear the POP, but there is no surge in plate current.


****************************************************
*** 73 from Radio AF4K/G3XLQ Gaithersburg, MD USA  *
**  E-mail to:  bry at mnsinc.com                     *
*** ICQ 6124470  ***
**  http://www.mnsinc.com/bry/                     *
****************************************************
AM International #1024, TENTEN #13582. GRID FM19. Using a SWAN 250 on 6m,
Other rigs: Valiant, DX-60/HG-10, FT-840, TM-261A, Ameco TX-62, Gonset Comm. III
TEN-TEN #13582, DXCC #17,763 Bicentennial WAS

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