[R-390] Re: [Collins] R-390A Filters

[Bill Abate]

After multiple tests I determined that my 4 KHZ filter was shot.  With 
nothing to loose I decided to open it up and I think I found a cause for 
the failure.  The input and output terminals a shunted with a 20 pf mica 
and a 200K resistor.  They were fine.  What wasn't fine was the filter 
itself.  It had separated into two pieces between the resonating discs 
and another one of the spot welds was half broken.

Collins had originally put a brown foam type substance in the body to 
provide a shock mount.  The foam had all but disintegrated into a goo. 
The filter was free to rattle around inside like a ping pong ball in a 
coffee can!  Somewhere in its life it must have been shocked, dropped, 
etc. and died.  If this failure is not peculiar to my filter the future 
could hold time bombs.  To correct this situation would take a lot more 
patience than I have.

If I wanted to test the rest of my filters (?) I would remove the 
filters and gently turn it upside down to see if I can feel any movement 
(without causing a failure).  If the filter needed new foam I would open 
the filter, remove the old stuff and put in new, reseal the filter and 
hope it still worked (connections are about #40 wire that is hard to 
see, let alone solder).  Definitely not something I would want to try or 
recommend.

Anybody have additional experience?

73,

Bill, K3PGB

Merle wrote:
> Hi Bill..
> 
> Read your post with interest ! I had the same problem with the same
> filter, I opened it up and ruined it ! It was not potted but a real mess
> inside. I'll watch, with interest, to see if there is a way to bring
> yours back to life.
> 
> Look for you on the CRA Net..
> 
> Merle
> 
>