[R-390] RE: Mechanical Filter Repair

[John Kolb]

Failures in mechanical filters could be of two types. Some
filters have foam supports that decompose into a gummy, sticky
mess that increases the attenuation, and I've heard that R-390A
filters do that, although very seldom, unlike Kokusai filters.
This would be easy to fix, once the filter has been opened.
A sudden failure such as you report, however, is much more
serious, caused by either a coil failing, or a mechanical
failure such as Tom Laird reported. I haven't seen coils fail
internally, although they would if C553? fails. I have seen
the connecting wire between the coil and the terminal break
or have a bad solder joint at the terminal. The wire can
be spliced and lengthened if it breaks in the middle or right
at the coil on the outside - unwind a couple of turns from
the coil to get something to splice to. A break at the coil
on the end going to the inside of the coil is best repaired
by replacing with a good coil from a different filter. If the
filter is broken, nothing is lost by trying to repair it.

A loss of signal in one filter position is not always the coil,
however. It occasionally can be the switch or the capacitors at
either end of the filter.

A 6th choice is to buy a used tested and plotted filter from
me, <http://members.cts.com/king/j/jlkolb> - I've just
added a number of R-390A filters - or a filter from that
auction place - about 80% of the filters I've bought there are OK.

John

On Wed, 18 Aug 2004, Dennis Pharr wrote:

> All:
>
> Many thanks for the responses to my question.  It looks like my options are
> the following:
>
> 1. Purchase a spare IF strip module from American Trans Coil($72) and hope
> that the 4kc filter is good.
> 2. Purchase a replacement filter through ER Mag ($175).
> 3. Purchase a new Collins filter from Inrad ($125) and still have to deal
> with the impedance matching issue.
> 4. Look into the cheap ceramic filters offered by Toko and Murata and also
> deal with the impedance matching issue.
> 5. And finally, try to repair the filter, but reports are that the success
> rate, had by others that have tried, has been very low.
>
> Right now I'm looking at pursuing options 1 and 4.  I think $72 is a
> reasonable price to pay for an entire IF strip module, even if some of the
> filters are bad.  Also, the Toko and Murata filters are cheap at about $2
> each and they would be fun to play with, although I don't expect to see
> performance equal to the mechanical filters.  All in all, I suspect I'll get
> what I pay for.
>
> Thanks again,
> 73
> Dennis Pharr
> WD5JWY
>
>
>
>
>
>
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