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Put it aside but don't give up on it.
How did you decide the IF frequency? When the IF has a crystal
filter the crystal determines the exact IF frequency but when there is
no crystal you just set the signal generator to the frequency defined in
the instructions, nearly always 455 Khz. The signal for aligning the IF
can be injected into the converter tube as per instructions, i.e. pin 8
through a 0.02uF cap. Actually, the IF can usually be aligned by feeding
the 455 signal into the antenna terminals. with the signal frequency at
about the middle of the dial. Set the signal generator for a weak
signal, you want no more signal than will overcome noise. Peak the six
adjustments to tune the IF to exactly 455 Khz and also adjust the BFO to
zero beat (also in the instructions. I don't think being off by a couple
of Khz is causing your problems but you might as well do it correctly. I
would go over the three IF transformers a couple of times to make sure
they are peaked and there is no interaction (should not be).
Now, what is going on here? A second receiver, or the SA, can
listen to the local oscillator. Make a sniffer loop to put over the
converter tube. check its frequency over the range on the broadcast
band. It should be 455 Khz _above_ the signal frequency at all points.
At the lowest frequency, say 540 Khz, the LO should be at 995 Khz. Check
it at three or four points up the dial. It should be reasonably close to
the signal plus 455 Khz all over. If you can't find it at the bottom end
start at mid point, or wherever you can receive some sort of signal and
tune down until it stops. What is the result of this? Since the
oscillator works at higher bands its not likely to be a short from dirt
or a bend in the plates but that is sill worth looking for. Make sure
you are not measuring the frequency wrong somehow. The problem is
impossible meaning something is being missed.
Poke at it some more and post back. I am fascinated by this and
don't mind at all trying to help. Lets save this antique, probably a
pretty good receiver when working and I suspect the problem is some sort
of illusion, look at it from a different angle and it may show up. DO
NOT GIVE UP.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998