[Hallicrafters] SX-28a questions

Mon Oct 22 14:53:58 EDT 2012

Hello John,

Found this <http://antiqueradios.com/forums/viewtopic.php?f=5&t=204873> in
Antique Radio Forums re: the mod.  Looks like the consensus was a sideband
slicer or a q-multiplier.

Yes, the darn things are intimidating!  My plan is to take it one component
at a time for now.

Best 73!
Jon, kb9wvk

On Mon, Oct 22, 2012 at 1:42 PM, John King <k5pgw at yahoo.com> wrote:

> Jon, the coax from the selectivity section might have been to connect an
> outboard Q multiplier or other outboard device. I have an original SX 28A
> standing by fr refurbishing. I am intimidated by the 90 pound monster. Good
> luck and keep us informed. 73, John, K5PGW
>
>
>
>
> ________________________________
>  From: Jon Miccolis <jon.miccolis at gmail.com>
> To: Hallicrafters at mailman.qth.net
> Sent: Monday, October 22, 2012 5:11 AM
> Subject: [Hallicrafters] SX-28a questions
>
> Hello all!
>
> I just brought home a late SX-28a (s/n HA36972) in what appears to be good
> cosmetic condition.  Front panel looks good and is relatively clean, all
> knobs are there, case is a bit rough but looks sound, missing bottom cover,
> no evidence of extensive tinkering or restoration (original caps, etc).
> All considered, so far anyway, it appears to be a good resto candidate and
> a suitable winter project.
>
>
>    1. The audio x-former has been replaced with an Archer universal output
>    x-former.  The audio output leads have been disconnected from the
> speaker
>    terminals and have been fed through the back of the chassis
>    2. There is coax soldered to a section of the selectivity switch and a
>    pin on the socket of the 2nd IF amp 6SK7 (V6).  This coax terminates in
> a
>    bnc connector on the back of the chassis
>    3. The antenna/ground terminals on the back of the chassis have been
>    removed and the above mentioned speaker wires feed through the opening
>    4. Bandspread dial indicator needs to be restrung
>    5. Previous owner (took receiver in on trade) recently replaced
>    rectifier and applied power to the receiver; did nothing further
>
> I got the thing home, blew the dust out of it, and hooked it up to a variac
> and brought up slowly over the course of a few hours.  No smoke, got noise
> out of headphones, s-meter stuck.  All in all, though, so far so good.
> After about 20 minutes at roughly 117 volts on the variac the receiver
> lost power.  No smoke, no sizzles, no smells.  Just lost power.  Checked
> the fuse and it was blown.
>
> A full recap is planned but slowly and one section at at time.  So I am
> going to start at the beginning; at the power supply section.  I plan to
> start with replacements for:
>
>
>    1. C41 and C44 (for 1st audio amp but in a shared can in power supply
>    section so mights as well replace now)
>    2. C47 and C48 (Cathode bypass and plate power supply output filter cap)
>    3. C49 (plate power supply output filter cap)
>    4. C51 and C52 (AC line bypass caps)
>    5. New fuse
>    6. line cord - three prong
>    7. test all tubes/replace as needed
>    8. Deoxit all contacts, switches, tube sockets, etc.
>
> Once the new line cord is installed, 7 caps replaced, tubes checked, fuse
> replaced, and contacts cleaned I would like to attempt another power-up in
> order to determine if the over voltage condition presumably responsible for
> the first fuse failure has been resolved.  Question is is this safe?  Is
> there a better way to do this?
>
> Also, are there any meaningful continuity tests that can be performed on
> the power transformer (primary to secondary for example) prior to applying
> power?  If T7 is shorted or open in any way then I have bigger problems
> than line cords and filter caps :)
>
> Thanks for the bandwidth and I look forward to your comments and
> suggestions!
>
> Best 73!
> Jon, kb9wvk
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