?

This has turned into a lengthy thread, but I think it is worthwhile as
more than one family of Hallicrafters receivers seems to have adopted
the unusual circuitry, at least in their schematics, and in their actual
implementations, if I am correct, maybe beginning with the S-40B.

Resolving this might be helpful to others who, in the future, come up
against this odd arrangement and wonder whether they should rewire things.

73,

Maynard
W6PAP

On 2/12/25 03:35, Maynard Wright via groups.io wrote:

It certainly looks as if there is a problem with the schematic, and I
thought that was the case, but I think now that the original schematic
is correct and that rewiring it to make it look "normal" will impair or
fail Bands 1 and 2.

My thoughts about the input circuit follow. This assumes that the
signal path is coupled between the two windings of L3 even though the
Hallicrafters schematics of the S-85 and S-40B don't show that. The
very good schematic of the S-40B by dexterdxer@... does show a
dashed line around the two windings of L3, which is, I think, a good
addition to the original schematic:

Band 4:

The signal passes through L1, with D/C as the the primary and B/A as the
secondary. As the primary is connected to antenna terminals A1 and A2,
the input may be either balanced or, by using the link between A2 and G,
unbalanced.

Band 3:

The signal passes through L2, with C/D as the the primary and A/B as the
secondary. As the primary is connected to antenna terminals A1 and A2,
the input may be either balanced or, by using the link between A2 and G,
unbalanced.

Band 2:

The signal passes through L3, with D/C as the primary and B/A as the
secondary. As the signal is passed from antenna terminal A1 through the
primary of L3 (terminal D) to ground (terminal C), antenna terminal A2
is left unused and only the unbalanced option is available. Switch S1A
leaves R65 open in this position.

Band 1:

The signal passes through L3, with B/A as the primary and D/C as the
secondary. As the signal is passed from antenna terminal A1 through the
primary of L3 (terminal B) to ground (terminal A), antenna terminal A2
is left unused and only the unbalanced option is available. Switch S1A
places R65 in series with input terminal B in this position.

Condensation of this scheme:

Band 4: L1 D/C primary B/A secondary
Band 3: L2 C/D primary A/B secondary
Band 2: L3 D/C primary B/A secondary
Band 1: L3 B/A primary D/C secondary

The circuitry between V1 and V2 is also a bit odd, but I think it is
also ok as in the schematic. But it uses an entirely different scheme
than does the input circuitry.

73,

Maynard
W6PAP


On 2/11/25 22:18, Richard Knoppow via groups.io wrote:

I need to take my own suggestion and redraw the circuits for the RF
amplifier.
It is usual for schematics to show coils and transformers in the
order they are used in the bands but the S-85 seems not to. In
particular the two low frequency bands seem to be reversed. Looking at
designations for the parts and alignment data tends to confirm this
to me.
If this is correct the third band down from the top of the
schematic is the lowest frequency band, i.e. the MW broadcast band.
Redrawing may make it clear what the resistor is. I can think of two
possibilities: one that is is to reduce gain. A common feature in
all-wave receivers since, at least in their primary market in the U.S.
signal strength on the broadcast band is often extremely high causing
overload and cross-modulation. Secondly; it may be to "spoil" the Q of
the resonator to broad-band it a little to improve fidelity. This is
also done fairly often in receivers with broadcast band capability. The
bandwidth can be increased a bit without reducing the image rejection
much. Neither of these may be the case but a circuit analysis will help
prove it.
I am sure Emmanuel feels as though we have stolen his ball and run
away with it. Perhaps he will have an insight as to the problem and
up-stage us all. What set me off was the suggestion that the design was
faulty even though its been used in at least two fairly mass-produced
commercial receivers. This still doesn't answer why the two bottom bands
don't work but redrawing the circuits may do that.
One can't ignore the converter stage either since if there is a
problem in tuning or the oscillator doesn't work the results in the
same, i.e. a dead or partially dead band.
Its always frustrating to encounter something like where the
equipment is very remote and one can't just have at it.

On 2/11/2025 6:37 PM, don Root wrote:

Maynard , there is one clue for band 2, that being that R6 will pull rf
?plate current thru L5… but then what.

Band 1 draws that plate current thru R26, C29 … but how does a signal
get to L6.

Looking at the alignment stuff layout, there is nothing unusual around
L6, so no clue there. At those frequencies we don’t expect ?invisible
gimmicks do we?

We will be in the loony bin soon! If we don’t get help from the Halli-
gurus ??….HELP!!!


--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998