"Smokey" wrote in message
m...
Hello Glowguys,

I am working on a Hallicrafters SX-25 that has a
specific li'l nuance (or better described, NUISANCE) and I
am hoping someone out there can help me.

The SX-25 has TWO RF COILS for the standard broadcast
band (Band 1) preceeding the First Detector/Mixer/HF
Oscillator. Both of these coils were disconnected prior to
my obtaining the rig for some unknown reason (the coils
are fine, I've got continuity through the primary and
secondary of each). HOWEVER I also own two other SX-25s
and when I compare this one to those I find the other ones
only have ONE RF COIL ahead of the First Detector/Mixer/HF
Oscillator for Band 1.

H-m-m-m-m.

One suggestion I received was that the circuit of the
early run SX-25s was very similar to that of the SX-17, so
I compared the SX-17 to the '25 however it shows the
antenna jacks connected directly to the 1st Detector/Mixer
and completely bypassing the RF AMP stages on its Band 1
(standard broadcast band).

My Band 1 is dead but I have goot perfecormance now on
Bands 2, 3 and even pretty good performance on 4.

Does anyone have an early run SX-25 and can tell me how
these coils are wired? I've experiemented with a lot of
logical combinations I thought might be possible but none
seem to bring in the ball game and neo-conservative
dingbat talk shows for me.

Every schematic I have ever seen for the SX-25 (including
those on BAMA and the originals I own) show only one RF
coil in use for the the standard broadcast band, so if
you've got an earlier schematic I WILL PAY MOOLAH for it.

Thanks for any help you can toss my way.

W9STB
I have the same schematics as you do, a Hallicrafters
1945 handbook from BAMA and a Rider's summary. Both show
that Hallicrafters used an arrangement that is common in
both H and other receivers with two RF stages , that is
by-passing one stage for the broadcast band. I suppose its
possible that both RF stages were used in early receivers.
The reason for by-passing one stage is mainly to avoid
overloading from the very strong signals often encountered
from broadcast stations and another is to broaden out the RF
bandwidth since this RX also has a broad IF response for
good fidelity from BC stations. I think there are other H
receivers which had such changes. Does the band switch have
the requisite contacts for an RF transformer between the two
RF stages? There should also be a trimmer capacitor for the
coil or perhaps scars from one that was removed.
I am trying to think of ways to find out what was there
in case an old handbook can not be found.
Hallicrafters seems to have changSed model numbers when
making significant changes in design, i.e. S-40, S-40A,
S-40B or S-20 and S-20R (R presumably meaning "revised").


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Richard Knoppow
Los Angeles, CA, USA