I was listening to my most modest boatanchor, an S-38E, at the
ktichen table when it suddenly, in mid broadcast, came on with a massive
raw AC hum on the output.
By way of diagnostics I downloaded the manual and schematic from
the BAMA site.
I changed out the 3 section filter electrolytic and the cathode
bypass on the audio out tube with new, tested caps. No help.
I checked the rectifier (35W4) and all other tubes for heater to
cathode shorts on a good Hickok tube tester. Replaced the rectifer with
the best of three available. Still hummed.
Recapped all caps in primary 117 vac to dc supply and audio output
stage. Still hums massively.
I've already got more in time and parts than an S-38 is worth in
this project. Anything obvious I should have thought to look at before
I give up ??