[R-390] Physical Location of C568 - C571

[David Wise]

There's no drawing or photo that I know of, but
the correct connection can be deduced from some
manuals.

The trimmers should be paralleled by fixed mica caps.
All of the fixed caps are 82pF except C507 and C516
on the 16kHz filter, which are 51pF.  So find the 51's;
the associated trimmer goes to the 16kHz filter.

(Note: Some 8kHz and 16kHz filters are special and
do not use the fixed output caps.  In this case, the
caps should be present but not connected.)

This information is not in the original TM 11-856A.
In TM 11-5820-358-35, it's Figure 15 (Modified
mechanical if. filters), on page 26.  (Someone added
this figure - without the page number - to my scan
of TM 11-856A.  I don't remember where I got this
scan.  It's dated October 4, 2001, and it's
44,335,104 bytes.)  In Y2K-R2 and Y2K-R3, it's
Figure 3-6, on page 3-16.

Dave Wise

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Jon Schlegel
Sent: Friday, April 24, 2009 8:12 AM
To: r-390 at mailman.qth.net
Subject: [R-390] Physical Location of C568 - C571

Hi all,

I'm assembling the topside mechanical filter compartment of a 390A IF 
module.  The documentation I have (TN11-856A) is not clear as the 
exact physical location of the trimmer caps, C568, C569, C570 and 
C571 that tune the output transducers of the filters.  The reference 
designators stenciled on the top of the filter shield box locate 
these trimmers at the top corners of the shield box when in fact the 
trimmers are mounted to a "plus" shaped bracket placing the trimmers 
"in between" the filters.  It would be just as easy to wire a given 
trimmer to either of two filters.

What is the correct relationship of these trimmers and their filters?


Regards,
Jon Schlegel WA3MVM