[R-390] building up a spare IF deck - filters?

[John Kolb]

I've seen Motorola and Dittmore-Freimuth filters that work fine, but
Collins has made many types of filters for many years so are the
real experts in the field.  I would use Motorola or DF if that's all I
had, but wouldn't try to find them in particular.

I don't think there were ever enough Motorola or DF filters around
for anyone to have an idea of their failure rate.

Dave Curry filters are modern mechanical filters in a case, along
with matching circuitry to match the low impedance of modern
filters to the high impedances found in tube circuitry.

R-390A's were also made with Clevite ceramic filters.  I believe many
of those were later replaced with Collins filters.  I would stay
away from the Cleveites.

You can poke around on my site and see some Collins filter curves
http://www.jlkolb.cts.com/site/mfcurves.htm
and also find some Motorola and DF curves on the for sale page
http://www.jlkolb.cts.com/site/fs_mf.htm
(It's an old site - very little for sale any more.)

John


At 07:11 AM 12/15/2008, you wrote:

>Hi,
>I'm starting to put together a spare IF deck to use for testing & 
>troubleshooting my R-390A (1958 all Motorola).
>I'm new at this hobby and am trying to learn as I proceed.
>I bought a scavenged 390A IF deck, all it has remaining on it are 
>the transformers, tube sockets,
>electrical connectors.
>The filters & BFO plus some other small parts are gone.
>I found a BFO with no problem. (but no bracket or coupler)
>I have found some different mechanical filters  for sale in various places.
>Not sure if I should get the standard Collins filters,
>or are the Dittmore-Freimuth filters any better from a mechanical design?
>  (is there any decomposing foam in the DF design?)
>I have also found references to Dave Curry - Longwave Products 
>filters, but they seem to be even more
>obscure than the D-F, so I'm guessing these are a very low 
>probability to find.
>(I have not found any of these for sale anywhere)
>What is the actual operational effect, the functional performance 
>difference between the
>different manufacturer's filter designs?
>Is it worth the effort to attempt to obtain non-Collins filters?
>Thanks,
>Frank



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