"Smokey" wrote in message
...

Hello Richard.

...and thank you for taking the time to share your
thoughts.

Indeed I am quite aware that the reason for the
bypassing of one of the RF stages was due to overload
problems.
Perhaps when I wrote my posting I had not yet discovered
that I was still sniffing out two distinct problems, which
I
subsequently have discovered.

First, some of the early SX-25s had two RF coils with
two trimmers. For whatever reason someone disconnected
both my antenna coil and the first RF coil. The antenna
coil wiring on the "generic" schematic available
everywhere is correct but the 1st RF coil portion is not
if you have an early SX-25 with two RF coils.
True, the broadcast band (Band 1) skips over the first RF
coil ostensibly to avoid the overload problems. I own two
other (later version) SX-25s and neither even is fitted
with the first RF coil "inside" the antenna-to-oscillator
chain. I have figured out the wiring and my SX-25s works
like gangbusters now.

Shorted turn were a common way of adjusting air core
coils. The shorted turn method probably lowers the Q a bit
but the range of adjustment does not have to be large.
Another method of providing for some adjustment was to wind
a few turns of the coil so they were separated from the main
section by a space and could be moved. The change in mutual
inductance would provide for some adjustment range. I don't
know how to calculate padding capacitors from memory but the
method will be found in books like the famous _Radiotron
Designer's Handbook_ or K.R.Sturley's book, both available
on the web. Personally, I would try the shorted turn method.
Again, there may be enough similarity in the later
Hallicrafters receivers to provide a clue. I think the
S-40/A/B was the replacement for the S-20.
Its something to be redoing the work of long dead
designers:-)


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Richard Knoppow
Los Angeles, CA, USA

WB6KBL