[Hallicrafters] SX-28a questions

[Jon Miccolis]

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