[Hallicrafters] SX-25 recapping question

[Rob Copeland]

when re-capping my sx 28 I had to carefully remove both rf sections and
partially remove the mixer and oscillator circuits in order to get at and
replace the capacitors & resistors. Just make sure you carefully mark every
wire you unsolder. I used a colorcoding system useing model paints. It's
virtually fool-proof because once dry the paint will not rub off. Take notes
also. It is not an easy procedure but well worth the effort. I would also
suggest that you replace the resitors as well. I found over 90% of the
resistors in my sx 28 to be out of tolerance (over 10%). anyway just my two
bits...

Good Luck! :)

Rob

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net]On Behalf Of Mike Everette
Sent: Sunday, May 21, 2006 5:23 PM
To: hallicrafters at mailman.qth.net
Subject: [Hallicrafters] SX-25 recapping question


Can anyone recommend a procedure for getting to the
two wax capacitors at the 6K8 osc-mixer socket in the
SX-25?

These caps are buried deep.  I was going to try and
remove the coil-mounting baffles, but it's so tight in
there that I can't even see how to get to some of the
leads that would have to be unsoldered.  I thought the
SX-28 was tough but this one seems worse.

There are 2 caps, an 0.02 uf on the screen and an 0.05
on the cathode (or is it the other way around...?).
Plus I need to get to the grid resistor on the
oscillator, as it is marked 50K but reads 78K to
ground.  That is a tad high.

The mixer cathode resistor in my receiver read 417
ohms to ground, and the schematic/parts list shows it
as 250 ohms; but when I looked at the resistor it is
actually marked 400 ohms.  I think my manual is dated
1945 but the receiver serial number seems to point to
mid 1941 production, judging by the info on the
Western Radio Museum web site; maybe the 250 ohm value
was a later revision.

If anyone has been into an SX-25 in this area
sucessfully, could you please share your experience?

By the way, darn near every 1/2 watt resistor in this
receiver read anywhere from 40% to 85% too high.  It
looks a lot different under there now, more like a
home brew project than a simple recap.

I can share something else, maybe a pitfall to avoid.
When re-using the 1/4 onch hex head sheet metal
screws, such as those that hold in the baffles and
secure other parts in these receivers, BE CAREFUL.
They are old and possibly suffering from corrosion.
They are either cheap steel, or in some cases maybe
aluminum; I found one that a magnet did not attract.
If they are overtightened even a little bit, even with
a regular nutdriver, the heads will snap off.  I had
two do this.  Fortunately I was able to back them out
using pliers, from the top of the chassis.  It would
be better to replace these old screws with more
durable ones, than attempt to reuse them.

Thanks and 73

Mike
WA4DLF

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