Bill Gunshannon wrote:

Do we have any R390 aficionados here? I have a problem
with an R390 that I am trying to revive after many years
in storage and hope this may be a known problem.

BFO does nothing. Tube is good and switch is providing B+
to the circuit. Doesn't seem to me that there is much else
that could go bad.

Any suggestions?

Has the unit been recapped or does it have original capacitors? There are
three paper caps next to the BFO PTO can on the IF deck and they go bad.

Put a coil of three or four loops of wire around the BFO tube and connect
it to a scope and see if the tube is oscillating. If not, make sure it has
the right voltages on the pins (the Y2K manual has proper voltage readings
with a modern DMM). If something goes wrong inside that BFO PTO can I don't
know what you do but there isn't a lot in there to go wrong.

While you have it open put a drop of turbine oil on the bushing to the
BFO PTO. And clean the big connector on the back of the deck and hit it
with Cramolin or some other good contact protectant.

If it were me I'd pull the IF deck out and ship it to Chuck Rippel for a total
rebuild, if that hasn't been done already. He does beautiful work.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."