A couple things I found when I reworked a BC-348R a couple years
ago....

1. A previous owner built a power supply on the bedplate for the
dynamotor, and hooked the outputs up the same way as the original power
supply. He ran the power through the AVC-OFF-MVC switch, just as it
was when the dynamotor was in place. When the set was designed, +28v
to the switch, ground to chassis. On my receiver, it was now one side
of the AC line running to the switch, the other side to ground. I
found this out rather spectacularly one day when I touched the chassis
of the receiver, and brushed up against something grounded. This
engendered a complete circuit trace to determine the problem....my
(temporary) fix was to run the cord to the primary of the transformer
with no switch...a little inconvenient, but better than getting
electrocuted.

2. I didn't see any mention of this...you may already know this, but
just in case...those plastic capacitors on the component boards are
actually paper caps, with all the problems inherent therein.