[Hallicrafters] SX-28A Recapping

[psturdivant n1ps]

I'm gonna chime in too.  I recapped both a 28 and a 28A.  I replaced all the
caps in the 28 but left some of the caps in place in the 28A in the RF
section.  I determined that the 28A RF section would involve the same work,
i.e., removing the shafts,, loosening the RF frame, etc.  Like some of the
others, the last few caps, all bypass caps in the front end, were not worth
the effort.

However, you do need to check the bias resistors in the RF deck area around
those first few stages.  Over time, the carbon resistors go high in value
and can affect the gain of the stages.

Good luck.  My 28A is my primary 75 meter receiver.  It is a great piece.

Pete
n1ps
----- Original Message -----
From: <W1gfh at aol.com>
To: <mikesmout at sympatico.ca>; <hallicrafters at mailman.qth.net>
Sent: Monday, January 13, 2003 11:53 AM
Subject: Re: [Hallicrafters] SX-28A Recapping


> Mike, I recapped all but the RF deck in my 28A and it's purring along
fine.
> While you are in there you might want to check the various power resistors
> (anything over 1 watt) and replace them if they look "iffy".  - Joe, W1GFH
>
> *Below is an email I got from Jeff Anderson a while ago regarding the same
> issue. Reading his insights might be of help.
>
> --
>
> When I received my 28A the easy caps had been replaced.  The RF deck had
not
>
> been done, and the caps around the push pull audio (obscured by P/S caps,
>
> P/S choke, tone choke, and output transformer) were still original brown
>
> waxys.  One of the caps in the push pull had failed, which took out the
>
> output transformer.  That's why I got it cheap.  While replacing the caps
in
>
> the audio section, I too looked at doing the RF deck, but decided that it
>
> was more of a project than I wanted to tackle.  Within six months one of
the
>
> screen bypass caps in an RF amp had failed, so I was left with no choice.
>
> I don't believe that there is any easy way to do it.
>
> On the top side, all the connections to the tuning caps must be removed of
>
> course, and on the IF side of the deck, each of the 'modules' has 4
>
> connections at feedthru terminals down near the screws.  Less obvious is
>
> that most of the modules have at least 1 wire coming out through a grommet
>
> on the P/S side that connect to different points to deliver high voltage
to
>
> the modules.  Also, most of the modules have a wire or two that pass
through
>
> grommets from one module to the next.  These are the tough ones.  As I
>
> recall, most of them can be reached, marked, and carefully unsoldered from
>
> the band switch.  In at least one case, I cut the wire rather than
>
> unsoldering it from the terminals on the RF coils, and repaired it later.
I
>
> was afraid of damageing the coils during desoldering.  Once the wires are
>
> all undone, and the shafts removed, the modules will come out.  I believe
>
> that I started at the rear of the receiver (1st RF), and worked my way
>
> forward.
>
> There are caps down in there that you can't even see without removing the
>
> modules.  While replacing the caps, I checked all the resistors and found
>
> that very few were within 20% of their original value.  In the end, I
>
> replaced all the caps, and all the resistors.  I also tested and replaced
>
> many resistors in the rest of the receiver as well.  If you choose such a
>
> radical course of action, I would recommend trying to duplicate the
original
>
> component placement as much as possible.  Due to short leads on some of
the
>
> replacement parts, I neglected this, and had some problems due to signal
>
> coupling.
>
> But when it was all said and done, it was a totally different receiver.
>
> Very sensitive, fairly selective, with nice audio.  The tuned frequency
>
> still drifts terribly, and the top band doesn't work due to a bad coil in
>
> the first RF amp (that's what I got the replacement deck for).  Both of
>
> these problems will require that I pull the RF deck again, so I'm in no
>
> hurry, but I really like this radio.
>
> As far as advice... It's a hard job.  If the radio works as it is, I would
>
> probably wait.  But brown waxys fail, and if you wait (and use the
>
> receiver), you will probably get your chance anyway.  As did I.
>
>
> Good Luck, and I hope some of this rambling helps.
>
> -- Jeff
>
>
> >Today I completed the "recapping" process on my SX-28A. Well, okay, I've
> >done all of the easy to get at ones, 24 to be exact. Now for recapping
> >in the RF compartment. I have read "Phils Old Radios" section on his
> adventure
> >in doing an SX-28. Can anyone tell me if the 28A is easier to recap than
> >its 28 counterpart! Sheesh, I'm thinking they are probably identical in
> >that aspect and can't wait to rip open the bowels of my beloved rig (NOT)
> >and unsolder all of those wires, take out all of those screws, disconnect
> >the bandswitch and antennae trimmer shafts (now I'm crying). Any
suggestions
> >and advice aside from what Phil has documented would be greatly
appreciated.
> >Thank you in advance!
> >
> >
> >
> >regards,
> >
> >Mike Smout
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> List Administrator: Duane Fischer, W8DBF **for assistance**
> dfischer at usol.com
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