[R-390] 4kc filter repair?

Fri, 09 Apr 2004 11:56:53 -0400

At 04:50 PM 4/8/2004 -0400, you wrote:

>Has anyone rebuilt a 4kc filter before?

Joe,

Yes, (but not me.)

>   I have also noticed a ..5db ripple across the top of the band pass on=20
> that filter.

That is so flat as to indicate the filter is kaput, which you know already.=
=20
Usually the ripple is much more than a half db  (or did you mean five db.?)

>   I supect that the foam inside the filter is bad

Likely. If a bit of foam gets onto the disks, the thing will be very lossy.

>   I am wondering if anyone has tried this and if so any tips?

I can't remember who told about doing this but there is a web site that=20
shows the process.  Now I cannot locate that web site.

Here are some parts of my notes file that may be of interest:

>From: John Kolb <[email protected]>
>To: Norman Ryan <[email protected]>
>Cc: [email protected], R-390 List <[email protected]>
>Subject: Re: [R-390] Mechanical Filter Repair
>
>On Wed, 24 Jul 2002, Norman Ryan wrote:
>
> > John "The Filter King" Kolb guesses the magnet wire size to be #36.  I
> > poked around with a Google search and found  DC resistance to be .4148
> > Ohm per foot at this site:
> > <http://www.mwswire.com/insdia2.htm>
> >
> > Any more hints, tips, experiences with mechanical filter repair from the
> > group?
> >
>
>Just measured 2 open filters and a loose bobbin and got wire
>diameters about 0.0062 and 0.0070 ("V and Y case filters),
>which would be 34 or 35 gauge enameled wire.
>
>The King  :)

Data on the filters is at:
http://www.angelfire.com/de/vk3kcm/filters.html

This site tells of inexpensive filters for the 74A-4:
http://www.albany.net/~bg/Mods/AMFilter.htm

INRAD, International Radio, Inc, sells new filters of many sorts:
http://www.qth.com/inrad/

In 2000, the following message started a 10- message thread on filter=20
rebuild. I suggest you search the archives with the subject and read them=
 all:

>From: [email protected]
>Date: Wed, 15 Nov 2000 05:35:22 EST
>Subject: [R-390] Mechanical Filter rebuild
>To: [email protected]

>I have a 4kc mechanical from a St Juliens rig which has a diaconnected
>winding. The cause of this as is so common, was from the inertial stress
>placed on the wire itself as the rig is transported. The original foam=
 shock
>absorbant material inside the filters is now likely to be in an advanced
>state of decay. I guess more of us will see this type of failure resulting=
 in
>dead positions on the selectivity switch. Interestingly, my other blue
>striper has a dis 2 kc filter.
>
>Now the Questions!
>
>1. Does anyone know how many turns are on the actuator windings of these
>devices
>
>2. Does anyone know how to form replacement windings. bothe the input and
>output windings are formed in two pies, about 0.2 inch diamater. The centre
>hole allows clearance for the actuator pin driving the resonant disks. The
>wire is (predictably) microscopically thin......I guess at 40 or 42 Wire
>Gauge (At those sizes the difference between AWG and BSWG is=
 impereptible!!!)
>
>Any comments would be welcome.
>
>Thanks
>
>Pete
>
>G4GJL

Roy

>thanks
>joe
>KE1MB
>[email protected]
>
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- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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