[R-390] Power connector R-390 (non-a)

[Dan Merz]

Hi,  I came home with an R-390 from the Puyallup WA swapmeet.  I think I was
doomed to have one if the price was tolerable.  Its serial number is 2064.
It has both covers, seems to have good mechanical mechanism,  panel
excellent, knob paint very worn and reportedly operating but weakly
according to the seller that I trust as a good guy.  It has ss diodes stuck
in the 26z5 sockets and a series of 5 ohm resistors (7 of them = 35 ohms)
stuck in the appropriate pins of the ballast tube socket.  I assume this
should be about 50 ohms instead,  as discussed here for the 390a,  as a
substitute for the 3tf7??

I don't have a power connector/cord - are these available from a known
source or does someone have an extra?

I was surprised that the tube sockets for the 26z5's are ceramic - was this
a heat consideration decision in the design ?  I usually think of ceramic
for high electrical insulating quality.

Other items seen at the meet,  an R-391 asking $800,  which I looked at
initially and thought was a  390 but later when I stopped to talk to the
seller I realized it wasn't a 390.   The tag indicated it was an RCA model.
It was missing the keys that go in the knobs and condition was undetermined
but it looked very good from the outside.   A 390a, asking $600 as I recall.
I don't know if either of these sold.  

Any help with the power connector would be appreciated, thanks,  Dan.