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

[JMILLER1706 at cfl.rr.com]

Is that because the older 390 (non A) did not use mechanical filters like te ones in the 390a?  I have experienced a similar failure in an 8 khz filter but it was heat related... the filter worked fine until the box warmed up and then would fail.  Some have talked about opening them up with blow torch or solder iron, then replacing the innards with a "new" Collins mechanical filter module, similar to what has been done with 75A4 filters by Curry Longwave.  Curry also sells "modernized" filters for the 390a... see:  http://www.r390a.com/html/Curry.html

----- Original Message -----
From: John KA1XC <tetrode at comcast.net>
Date: Thursday, December 9, 2004 1:56 pm
Subject: Re: [R-390] Re: [Collins] R-390A Filters

> >  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.
> 
> I beleive you are right Bill, this is a not uncommon failure, and 
> as the
> decades progress so will the deterioration of the foam mounts. 
> It's almost
> certain that at some future time the mechanical filter failures will
> approach the frequency of molded capacitor failures, and the very 
> thoroughR-390A restorer will then be faced with re-filtering in 
> addition to
> re-capping :^(
> 
> > 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.
> 
> Too bad these filters weren't plug-in, then the above efforts 
> might be
> worthwhile.
> >From my experience the filter loss starts to increase rapidly 
> just before
> failure. One R-390A that I brought home from a flea worked quite 
> well when I
> got it, but as it was worked on and it got moved around and over 
> on the
> workbench I noticed that it was loosing sensitivity only in the 4 KC
> bandwidth. first a few db, then a few more, then 20 dB, then dead. The
> filter was replaced but I haven't done a post mortem on it.
> 
> So I'd say that the state of the filter innards in any 390A is 
> indeed a crap
> shoot, even in the multi-kilobuck "'museum quality" radios that 
> pop up now
> and then for sale. The only thing I do different now is to try 
> minimize any
> mechanical shocks or vibration when moving or transporting a 390A, for
> example putting it on a cushy mat or blanket when transporting one 
> in the
> back of a car or truck, not for the sake of the tubes but for the 
> filters.It's ironic that although the R-390 is a much older beast 
> than the average
> R-390A it is not as fragile in this respect.
> 
> 73,
> John
> 
> 
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/faq.htm
> Post: R-390 at mailman.qth.net
> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>