[Johnson] FW: [Boatanchors] Valiant Troubleshooting Question

[Gary Schafer]

Reposting this for Roy Morgan:

-----Original Message-----
From: Roy Morgan [mailto:k1lky68 at gmail.com] 
Sent: Tuesday, December 30, 2014 7:55 PM
To: Gary Schafer
Subject: Re: [Johnson] [Boatanchors] Valiant Troubleshooting Question


On Dec 30, 2014, at 7:36 PM, Gary Schafer <garyschafer at largeriver.net>
wrote:

> The first thing I would look for is a bad loading capacitor 

Gary,

My posts to both Boatanchors and Johnson lists are being held for moderator
approval due to my not being a member.  Despite the fact that I get posts
from both lists.

Would you post my reply to one or both lists?  Thanks:


On Dec 30, 2014, at 7:36 PM, Gary Schafer <garyschafer at largeriver.net>
wrote:

> The first thing I would look for is a bad loading capacitor on the tank
> output. 

Bingo!

A known failure point in the Valiants is the supplementary fixed loading
capacitors.  They are sandwiched silver mica caps that are encased in wax.
They are known to fail, presumably with shorts or high leakage.  Since they
are in high RF current service, ordinary mica caps will not perform
correctly, so be careful in picking replacements.  

There two sets of four caps in series parallel - 
C39A, B, C, and D are each 330 pF form a total capacitance of 330 pF and are
used in only some band positions.

C 38A, B, C and D, each 150 pF for a total capacitance of 150 pF are engaged
on only one band position.

(I have not doped out the loading cap switch functions so this explanation
is only partially complete.)

In addition, the Output Coupling switch engages one or more of four
additional caps, C41 and C42A, B, and C.

It could be that only C41 and C42.. are the ones I describe and subject to
failure, so  be careful in taking what I suggest here as accurate.

Roy

Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958