Finally got one of the three R-4A receivers working well and it's now in
the shack. Here's the status:
R-4A #3781: A 13-tube, the second-nicest of the three, re-capped and now
working just fine. The only issue with this one was a REALLY warbly PTO.
Since #3735 (see below) was quite stable I swapped out PTOs and got 3781
checked out & fully aligned.
R-4A #3735: Another 13-tube and the worst of the three (the chassis looks
REALLY bad, chicken coop storage?), this one has a thoroughly hosed-up
preselector drive that I need to rebuild including turning a new SS center
shaft on the lathe. It also now has a warbly PTO (see above) but before I
swapped out the PTO it worked fine except for the preselector drive. The
chassis will make a good test-bed for trouble-shooting & fixing the PTO
assembly.
R-4A #5757G: An 11-tube, this unit looks almost new inside and out and a
chassis this clean has got to be VERY rare. Unit has been fully re-capped
and after a 30-minute warm-up it aligned just fine. It works great except
for two things:
(1) An intermittent that shows up after an hour or so that causes
signal levels to drop about 20 dB for a few seconds then pop back in. A burst
of static, switching to STBY and back to RCV, or opening up the bandwidth
to cause a "burst" of signal will correct the drop, but then after several
seconds it will drop again (but it self-corrects, the drops, then
self-corrects.....most annoying). The drop is visible on the S-meter as well
as
being audible. Tube replacement doesn't do a thing for it. Replacing the
damaged tube socket for V4 didn't, either.
(2) Seems to have a little distortion in the AM audio. Haven't
searched for the cause yet.
2B #2052: Has worked great from the day it arrived and I haven't had to
touch it. It's due for a re-cap (kit is on hand) and I'll run through the
alignment, and since it lost its place on the operating desk to R-4A #3781
tonight I'll probably tackle it fairly soon. It shouldn't need much other
than the new caps.
Problems notwithstanding, it's pretty amazing that these 40+ year-old
receivers can be made to work so well after all these years.
73/arf,
Paul, K4MSG
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