Not a lot of help maybe, but when my SX-28A mains transformer burned out I
had Danbury Electronics here in the UK make a replica, and they did a nice
job, incorporating the 115/230 volt switch and top cover onto their own
laminations and core. Cost was 100 GB pounds, not cheap but the RX is worth
it. I tried two transformers from two junker RXs before going to Danbury,
wish I'd saved the hassle as I found the two transformers in the junkers had
faults too. Danbury reported that the wax in the original had basically
turned to a sort of dust, they believed that the wax was organic, not
mineral.

73

Roger/G3VKM



"Tom" wrote in message
...
I bought it last year and restored it because my Elmer had one during
the early '50's and it always seemed the thing to have. I enjoyed the
restoration process (skiped the caps in the one RF section) and
alignment and had it working fine. Then the 5Z3 rectifier lit up
brightly a couple of times upon turn-on and then later, it blew a
fuse.
I recapped an SX-28 and did the usual cleanup etc and then realigned it
with care. All the voltages were within 10 to 15% and it worked well for a
few months. Then the 5Z3 rectifier lit up with a flash twice after it had
been off for a couple of weeks. Then while operating it blew a fuse. At
that point I replaced the fuse and it blew immediatly. I then used a Variac
and ampmeter and noted it would draw an amp with only 5 to10 volts on the
transformer primary.

I unhooked the caps on the line side, pulled the rectifier and jumper plug
in the rear to isolate the transformer and it will still draw an ampere
with only 5 volts on the primary. The line cord is not shorted and the
primary is not shorted to ground and it does measure low resistance ( a
couple of ohms) end to end which seems normal.

It appears the HV secondary is shorted - it measures 19 ohms to CT on one
side and 16 ohms on the other to CT and 3 ohms end to end. No shorts to
ground.

I have a parts SX-42. Do you know if there are any problems in using the
power transformer from the SX-42 in the SX-28? They measure physically
about the same and the schematics are the same but I don't know about the
power capabilities. Do you have the transformer numbering for T7 or the
SX-28? Any advice on the substitution?

Thanks for the help and guidance.

Tom Ruhlmann, W9IPR
262-377-6945