[Collins] KWM-2A Filter question

[Dr. Gerald N. Johnson]

On Wed, 2006-10-04 at 21:19 -0400, TVComlGuy at aol.com wrote:
>  Good evening to the group,
>  
> I have a RE KWM-2A that has a plug in filter.  The number is F 455 FB  21 
> 5WZ.  The Collins part number is,  526 9448 00.  I can't find  any information on 
> this filter and the manual I have says it should have a wired  in filter.  
> The rig doesn't work, so I question the filter.  I do get  a reading across the 
> two coils in the filter.  Any help would be  appreciated.
>  
> 73,
> Ron, KB0WAR
> 
> Post: mailto:Collins at mailman.qth.net
> 
The F455FB21 is the low priced version of the F455FA21 that was used in
later rigs.

The filter is common to transmit and receive and so its working is
critical. You could test by connecting a small capacitor (10 to 50 pf)
between the hot pins on the filter sockets. However the three
oscillators are also common to transmit and receive as is at least one
IF stage. Loss of any will kill transmit and receive as will lack of low
voltage and maybe bias from the power supply. Without bias T/R switching
gets messed up. Be sure the crystal board select switch is on a board
with a crystal in the socket for the band you are testing on. Check to
be sure the PTO is connected to the radio, there is a provision for
using an external PTO that disconnects the internal PTO and runs it to a
switch in the external PTO for PTO selection. Then one of the BFO
crystals could be bad as could a number of IF and mixer tubes. The VOX
relay could be stuck in transmit by the failure of the VOX relay tube
cathode bias resistors (2 each 33K 2w in parallel from +275 to that
cathode).
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer