HELP!! Valiant doing sneaky things!!

[Brian Carling]

Never mind - I finally fixed it!

One of the 20K 10 watt divider resistors for the HT+ / B+ was
completely OPEN!

Still not sure WHAT was ARCING but it's FIXED Now!!

Back to CX!!

On  1 Feb 98 at 13:06, Brian wrote:


> 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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****************************************************
*** 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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