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

"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


Hi Vern,

Have you tried wiring it like the schematic you have?


--
Regards
B.H.
Hill Amplification
http://hillamplification.com

Brian's Radio Universe
http://webpages.charter.net/brianhill/500.htm

Hi Brian,

Thanks for your suggestion. But that was one of the first things I tried and
it left one RF coil unwired.

Anyway, I have been plugging away and I think I have it wired correctly...at
least it seems to work well wired this way. I am redrawing tyhe schematic
for the SX-25 to incorporate the two coils and if anyone is interested drop
me an SASE at my QRZ.COM address.

Keep 'em glowing!

W9STB

"Brian Hill" wrote in message ...

"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


Hi Vern,

Have you tried wiring it like the schematic you have?


--
Regards
B.H.
Hill Amplification
http://hillamplification.com

Brian's Radio Universe
http://webpages.charter.net/brianhill/500.htm

"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").


--
---
Richard Knoppow
Los Angeles, CA, USA

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.

The second problem...that my BAND 1 (broadcast band) was completely
dead. I traced that to a missing jumper between the oscillator coil and the
switch.

I am now experiementing with improving the Band 4 performance. Adding
the shorted coil of wire to the RF and oscilllator coils is one way to go
but I am not convinced that, with slight rewiring of the coil chain I can't
provide an easier method of alignment by adding its own padding capacitor
for Band 4. Incidentally, every SX-25 I have owned...including this early
version I am now working on...have had the additional inductive turns
already added. In one case the coils were all modified and sealed with
either wax or Q-dope and then became covered with sludge from being
submerged in a flood 60 years ago; so I know that SX-25 owners in the 1940s
and 1950s were aware of the problem with IF tracking on Band 4 way back
then. Adding the shorted turn to the coils only flattens out tracking from
the bottom of Band 4 to about 30-35 MC anyway, so I am not convinced I can't
come up with a better way. Any thoughts on adding a discreet padder will be
warmly welcomed!

Thanks again for your thoughts and keep the spirit of glow alive. I am
quite sure this antiquated, simple and humble technology will still be
working long after much (most?) of today's junk technology has failed
irrepairably.

My best,

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").


--
---
Richard Knoppow
Los Angeles, CA, USA

"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:-)


--
---
Richard Knoppow
Los Angeles, CA, USA

WB6KBL

Smokey wrote:
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 had one of these about 30 years ago I bought at a yard sell I think
it actually had three RF coils. It had one for the antenna, one for
the first preamp, and one for the second preamp stage. I took it to a
guy in Willacoochee, Ga to get it fixed. He took a few voltage
measurements, replaced a couple of tubes and resistors and tuned it
up. I think he could tell what was wrong with it from the way it
smelled. Unfortunately it and my S40B were both stolen out of storage
about 5 years after I got it. The S40B was in near perfect mint
condition with all the origonal Hallicrafter tubes.

Jimmie