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?

bill
KB3YV

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."

On 11/7/18 9:39 AM, Scott Dorsey wrote:
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?

At this point, 100% original. And the only thing that isn't working
is the BFO. It is still an amazing receiver (my use of the R390 goes
back to my 70's Army days when we used to listen to WABC from Germany
on those late nights in the AN/GRC-26D!!)

There are
three paper caps next to the BFO PTO can on the IF deck and they go bad.

I'll look at that but I would be surprised if those were bad while
everything else was still OK.


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.

I'll try a scope. I tried a frequency counter and it shows nothing, but
may not be enough of a signal when so loosely coupled to pick it up.

If not, make sure it has
the right voltages on the pins (the Y2K manual has proper voltage readings
with a modern DMM).

I would like to do that but I would have to make one of those tube
extenders in the manual.

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.

Well, I read about those betting broken but mine seems OK. I
haven't opened it yet but I could. I remember someone saying
they reheated solder joints in theirs and it fixed this kind
of problem. Of course, I have a carcass for some spare parts
and the IF section is one that I still have.


While you have it open put a drop of turbine oil on the bushing to the
BFO PTO.

I tend to use Teflon lubricant for this. Or Lubriplate. I have
found both to be good for electronics.

And clean the big connector on the back of the deck and hit it
with Cramolin or some other good contact protectant.

Again, not suspect in this case at other things would be affected
and right now the BFO is the only thing not working.


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.

Yeah, and if I had that kind of money I would just buy another
one that was already rebuilt. :-) I'm pretty much stuck doing
this myself as the only thing I can afford is the wisdom other
people offer.

If I determine what the problem is I will try to let other people
know as I am sure I am not the only one trying to revive these
great old radios. (Yes, I have more than one. This is just the
first one I have decided to dig into.)

bill
KB3YV


bill