In article ,
says...
"Ken Scharf" wrote in message
...
Casual Fool wrote:
On Fri, 16 Dec 2005 23:06:46 -0500, Ken Scharf
wrote:


I have a new in the original box F455N20 collins filter
(from R390A) that I got at a hamfest many years ago
and stored it away for a 'future project'.

I dug it out recently and was examining it when I noticed
that as I rotated it in my hand I could feel something
inside shifting back and forth. I never noticed this
before (the filter was NEVER dropped in my care and
has remained packed in the original packing material
all this time). Is this normal for this type of filter
or might the unit be defective?



Hi Ken, I had a similar problem with an F455 XXXX 05 mechanical filter
for a 75S-3B/C receiver. When I would switch it in, the insertion loss
was 20 dB plus. Since I figured I had nothing to lose, I carefully
took the filter apart, and as I recall, there are three wires that are
spot welded to a row of resonating discs, and my filter had some
busted connections on one row of the resonating discs. I knew I could
not fix the filter, per say, but since I bought the 75S3-B from the
original owner, he could have very well dropped the filter, and then
installed it... I propose this for your filter. Since I haven't taken
apart a R390A filter, plug the thing in, and see if there is any
insertion loss. It may be that in your filter, which I presume is in a
round package, like a 75A-4, was affixed on either end, where the
input and output transformer(s) connect to the resonating discs, may
have been held in place with some foam or glue to keep the discs from
moving. I have seen in some Japanese mechanical filters they use a
foam substance that degrades over the years, however, I'm not sure on
the R390A filter.. So, plug the darn thing in a good working receiver,
and see if it works.. If its busted, then you've only wasted a few
minutes.. If your in dire straits, and need a new filter, or a used
NOS filter, there are plenty out there.. BTW, I haven't known or heard
of anyone that has really fixed a Collins Mechanical Filter with
busted resonating discs where the stadia wire has broken loose from
the discs... Good Luck OM es Best 73.. Tony WB8MLA, near Cleveland,
OH...
Thanks for the info.
This filter is from the R390a and is normally soldered into the circuit.
It does not have terminals that can 'plug in', the filter is mounted under
the chassis in a bulkhead that shields the input from the output. The
unit I have came in the original Collins box and was sold as a spare.
I have another Collins filter, I think the part number is FA455N27 that
is the usual plug in package with three pins on each end, probably from
an S line rig. This filter makes no internal sound when handled, so it
is still in good shape. I was going to use one of them in a homebrew
rig and the older R390 type has a 2.0khz bandwidth vs the 2.7khz bandwidth
of the newer filter.

If these filters can go bad just sitting in the original box in a low
humidity environment, I wonder how many R390A's now have rotting filters?

Large file (about 300 pages) ... from R390A group (Chuck Ripple) -- just has
filter and IF comments, repair suggestions, tips, "pearls", etc:
http://209.35.120.129/Pearls/IF-deck-tips.pdf

Wow... that file is amazing. R390 people are actually harder-core about
service, documentation, and product history than the vintage-Ferrari
nuts I have known.

-- jm

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