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