I am trying to resurrect a rather threadbare military surplus
National HRO 60 receiver that I got from a seller on ebay. It came
with a single D coil set, which turned out to be a dud. The only other
HRO 60 coil set I currently is a B coil set, so I have been using coil
sets from a working HRO 50T to troubleshoot this rig on the lower
frequency bands. The coils I currently have a
HRO 50 "A" (14 to 30 Mhz)
HRO 50 "A" (14 to 30 Mhz) (spare)
HRO 50 "B" (7 to 14 Mhz)
HRO 50 "B" (7 to 14 Mhz) (spare)
HRO 50 "C" (3.5 to 7 Mhz)
HRO 50 "C" (3.5 to 7 Mhz) (spare)
HRO 50 "D" (1.7 to 4 Mhz)
HRO 50 "E" (900 to 2050 Khz)
HRO 50 "F" (480 to 960 Khz)
HRO 60 "B" (7 to 14 Mhz)
HRO 60 "D"(1.7 to 4 Mhz) (dud-not currently working)
After replacing all the paper caps and about 25 resistors that had
drifted seriously out of tolerance (some as much as 50% to 100% off
correct values) I now have a working radio. It works surprisingly well
considering where I'm at in the restoration process (no alignment
attempt has been made yet).
It has one curious problem though....When I plug in either of the two
HRO 50 "C" coil sets ( the only ones I've tried so far, since I've
been working on the receiver at night), the dial calibration is way
off, by about 300 kHz. Thus, WWV shows up at 5.3 Mhz on the dial. Plug
the same coil sets into the HRO 50 and the calibration is right on the
money, so it appears that both my "C" coil sets are properly
calibrated.
I have already tried replacing the mica caps in the HF oscillator in
the off-chance that something there was amiss, but the symptoms did
not change.
Now, I already know that the HRO 50's "A" and "B" coils will not work
in a 60 due to the second converter that kicks in at those frequency
ranges, and I also know from reading previous posts to this group and
elsewhere that HRO 50 coil sets for frequencies below 7 Mhz WILL work
in a 60.
My question is, can the lower frequency coils from an HRO 50 be
expected to behave exactly the same in an HRO 60 as they do in a 50
(same dial calibration in particular), or is there some subtle
differences that makes realignment of a HRO 50 coil set necessary
before it will work perfectly in an HRO 60?
-Scott
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