?

“When it comes to the switch area, that schematic is spinning my head”

?

Glad it is not just me…… ?

?

I have not had time to get back to this, maybe tonight.

?

I believe it is in the 6V6 area because when I pull the 6SA7 the symptom remains. Maybe the choke has some leakage to ground? I was going to pull it last night and check it on my Sencore inductance tester. Got side tracked and didn’t get there. I’ll try tonight.

?

Tom

W3TA

?

I looked at both (S-40B and S-85) schematics again. The antenna
stage is different. The S-85 has a broad band plate load R-26, C-29
rather than a tuned circuit. The coupling appears to come through C-10
which feeds a tuned circuit in the grid of the mixer tube. …. +++++++++++++++++

?
?

?

Hi Jim

Re paragraph 1:? ?I would not be surprised about the talking, but can that cause 120 cycle hum?

Re paragraph 2: ?I agree, and there must be lots of return currents from B+ running to and thru the chassis, and chassis connections are rarely soldered, and to top it off, the schematic gives no hint as to ?the common wiring running to a chassis connection, so if one chassis connection opens a bit, what all lifts above the chassis common. After 70 years, there is lots of opportunity for corrosion.

Thinking out loud about the original complaint, hum would not seem to be from the B+ into the plates,? since there is no hum in one switch position, but it might be getting into 1 or both 6V6 grids, but it would seem to be both. When it comes to the switch area, that schematic is spinning my head. ?I would probably try to poke around with a scope and a high impedance probe. So often hum comes when there is an open connection from a lower impedance source signal wire. With so many schematic connections to the plate and choke etc it is hard to speculate on the real wiring. This is likely no help at all, but I tried.

?

?

--
don??? va3drl

I looked at both (S-40B and S-85) schematics again. The antenna
stage is different. The S-85 has a broad band plate load R-26, C-29
rather than a tuned circuit. The coupling appears to come through C-10
which feeds a tuned circuit in the grid of the mixer tube. This, and the
difference in the antenna coupling, suggests that the idea was to have
relatively low gain and broad bandwidth on the broadcast band. That sort
of arrangement is made on many all wave receivers. It is because
broadcast band signal strength is often very high and the fidelity of
the response is improved. Generally, image response is adequate on the
broadcast band with minimal selectivity (as in five tube AC/DC sets).
C-10 will also couple on the other bands but likely, as suggested,
will be swamped by the LC or transformer coupling there. Not sure of
this analysis.
Now, I wonder if Emanuel (sp?) can try an experiment. If he is
getting any response on the two low bands try shorting the A1 terminal
to ground and see what you get from A2. Not sure what this will prove
but maybe whether there is actually coupling there.
Second experiment: If he has a grid-dip meter perhaps it can be
used to induce a signal into the RF transformers. What I want to know is
if there is coupling between the two HF band coils L-1 and L-2 and the
coils with the two low bands on it L-3. The question is whether there is
enough mutual inductance between L-1 and L-2 to L-3 to complete the
circuit for A2 and act like a primary coil.
On a typical balanced input a single wire can be coupled to either
antenna terminal with the other going to ground with indentical results.
I am just wondering if there really IS a balanced input on the two
lower bands.
Actually the ability to use a balanced input on the broadcast band
is useful because one can use a loop antenna and make use of its
directional properties. A loop CAN be used on an unbalanced input but
there will be stray coupling so the directional property will be
disturbed. Anyway, I think its easy to find out of the A2 terminal
actually does anything on the two low bands and might provide a clue.

On 2/15/2025 1:16 PM, Maynard Wright via groups.io wrote:

Yes, C38 in the schematics of both the S-85 and the S-40B is a gimmick
for coupling the BFO. I wrote "CW oscillator" but should have written
"BFO."

73,

Maynard
W6PAP


On 2/15/25 13:08, Richard Knoppow via groups.io wrote:

I will have to look at both schematics again but think there is a
"gimmick" in one or both for coupling the BFO.

On 2/15/2025 8:57 AM, Maynard Wright via groups.io wrote:

Hi, Emanuele,

There is a gimmick in the S-85 schematic and parts list, C38, that has a
capacitance of 2 mmfd (pF). It should, ideally, be a twisted assembly
just about 10 percent shorter than is required to emulate C62 in the
S-40B if you want to check what a gimmick of about the right size ought
to look like.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

?

Yes, C38 in the schematics of both the S-85 and the S-40B is a gimmick
for coupling the BFO. I wrote "CW oscillator" but should have written
"BFO."

73,

Maynard
W6PAP


On 2/15/25 13:08, Richard Knoppow via groups.io wrote:

I will have to look at both schematics again but think there is a
"gimmick" in one or both for coupling the BFO.

On 2/15/2025 8:57 AM, Maynard Wright via groups.io wrote:

Hi, Emanuele,

There is a gimmick in the S-85 schematic and parts list, C38, that has a
capacitance of 2 mmfd (pF). It should, ideally, be a twisted assembly
just about 10 percent shorter than is required to emulate C62 in the
S-40B if you want to check what a gimmick of about the right size ought
to look like.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

I will have to look at both schematics again but think there is a
"gimmick" in one or both for coupling the BFO.

On 2/15/2025 8:57 AM, Maynard Wright via groups.io wrote:

Hi, Emanuele,

There is a gimmick in the S-85 schematic and parts list, C38, that has a
capacitance of 2 mmfd (pF). It should, ideally, be a twisted assembly
just about 10 percent shorter than is required to emulate C62 in the
S-40B if you want to check what a gimmick of about the right size ought
to look like.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Hi, Emanuele,

There is a gimmick in the S-85 schematic and parts list, C38, that has a
capacitance of 2 mmfd (pF). It should, ideally, be a twisted assembly
just about 10 percent shorter than is required to emulate C62 in the
S-40B if you want to check what a gimmick of about the right size ought
to look like.

?

It seemed to me to begin with that C62, or an equivalent gimmick, ought
to couple the signal adequately but that its value might not be very
important. But if C62 is very low reactance, the paralleling tuned
circuits won't have much effect on the passage of the signal from V1 to
V2. If C62 exhibits a very high reactance, essentially no, or at least
very little by stray coupling, signal will be passed for Band 1. In
addition, the value of C62 might act in parallel with the various tuned
circuits acting for Bands 1 through 4 to affect how they adjust and the
value of C62, or the equivalent gimmick, might need to be somewhat close
to the 2.2 pF value specified.

73,

Maynard
W6PAP

?

Hi, Emanuele,

There is a gimmick in the S-85 schematic and parts list, C38, that has a
capacitance of 2 mmfd (pF). It should, ideally, be a twisted assembly
just about 10 percent shorter than is required to emulate C62 in the
S-40B if you want to check what a gimmick of about the right size ought
to look like.

C38 couples the CW oscillator signal from the junction of pin 3 of V5
(6SC7), R29, and C55 to pin 4 of V4 (6SK7).

The S-40B also uses C38, specified in the S-40B parts list as 2 mmf but
labeled on the schematic with "1," implying 1 pF.

Incidentally, Note 2 in the S-85 schematic states that all capacitor
values are in "MMF" unless otherwise specified. In the parts list, C38
and others are specified in "mmfd." The S-40B parts list uses "mmf" and
"mfd."

73,

Maynard
W6PAP

Hi, Emanuele,

There is a gimmick in the S-85 schematic and parts list, C38, that has a
capacitance of 2 mmfd (pF). It should, ideally, be a twisted assembly
just about 10 percent shorter than is required to emulate C62 in the
S-40B if you want to check what a gimmick of about the right size ought
to look like.

C38 couples the CW oscillator signal from the junction of pin 3 of V5
(6SC7), R29, and C55 to pin 4 of V4 (6SK7).

The S-40B also uses C38, specified in the S-40B parts list as 2 mmf but
labeled on the schematic with "1," implying 1 pF.

Incidentally, Note 2 in the S-85 schematic states that all capacitor
values are in "MMF" unless otherwise specified. In the parts list, C38
and others are specified in "mmfd." The S-40B parts list uses "mmf" and
"mfd."

73,

Maynard
W6PAP


On 2/15/25 08:14, Maynard Wright wrote:

Hi, Richard,

Yes, that's exactly as it is in the S-40B, in the schematic and in the
receiver.? It's C62, a 2.2 pF cap (2.2 mmf in the S-40B parts list).

But the S-85 lacks that cap, in the S-85 schematic, the S-85 parts
list,
and in Emanuele's S-85.

So Emanuele added a twisted wire gimmick capacitor to his S-85 where
C62
is in the S-40B and saw a significant rise in signal levels on Bands 1
and 2.

My thought is that by adjusting the capacitance of his gimmick, or by
replacing it with a 2.2 pf capacitor, he might make it possible to
achieve a correct alignment of Bands 1 and 2 of his S-85.

I think that it's unfortunate that the Hallicrafters schematic of the
S-40B labels C62 as just "2.2."? My first thought was 2.2 uF, but the
S-40B parts list shows 2.2 mmf.

73,

Maynard
W6PAP


On 2/14/25 20:30, Richard Knoppow via groups.io wrote:

Very interesting Maynard. I am not sure I am seeing this straight
but it appears that there is an RC load on the RF tube coupled
via the
2.2 uF cap to the tuned circuit of the mixer grid. Should result
in a
fairly low gain and fairly broad tuning. That might be desirable
for the
broadcast band I am still not sure how the antenna coupling
works for a
balanced input.

On 2/14/2025 6:45 PM, Maynard Wright via groups.io wrote:

??? Hi, Richard,

??? You are right about the two small caps. But trace carefully
what S1B
??? (front) is doing when set to Band 1. The RF signal is
passed from the
??? plate of V1 through R4 and down to R26/C29. It cannot
appear below
that
??? RC combination because the B+ line should be at ground for
RF. So
??? without C62, there is no path for RF forward from V1, at
least in the
??? schematic.

??? So I wonder whether Emanuele might achieve good results
across the
full
??? ranges of Bands 1 and 2 by adjusting the amount of
capacitance his
??? gimmick provides or by using a 2.2 pF cap as in the S-40B.

??? 73,

??? Maynard
??? W6PAP


--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Hi, Richard,

Yes, that's exactly as it is in the S-40B, in the schematic and in the
receiver.? It's C62, a 2.2 pF cap (2.2 mmf in the S-40B parts list).

But the S-85 lacks that cap, in the S-85 schematic, the S-85 parts list,
and in Emanuele's S-85.

So Emanuele added a twisted wire gimmick capacitor to his S-85 where C62
is in the S-40B and saw a significant rise in signal levels on Bands 1
and 2.

My thought is that by adjusting the capacitance of his gimmick, or by
replacing it with a 2.2 pf capacitor, he might make it possible to
achieve a correct alignment of Bands 1 and 2 of his S-85.

I think that it's unfortunate that the Hallicrafters schematic of the
S-40B labels C62 as just "2.2."? My first thought was 2.2 uF, but the
S-40B parts list shows 2.2 mmf.

73,

Maynard
W6PAP


On 2/14/25 20:30, Richard Knoppow via groups.io wrote:

Very interesting Maynard. I am not sure I am seeing this straight
but it appears that there is an RC load on the RF tube coupled via the
2.2 uF cap to the tuned circuit of the mixer grid. Should result in a
fairly low gain and fairly broad tuning. That might be desirable for the
broadcast band I am still not sure how the antenna coupling works for a
balanced input.

On 2/14/2025 6:45 PM, Maynard Wright via groups.io wrote:

??? Hi, Richard,

??? You are right about the two small caps. But trace carefully what S1B
??? (front) is doing when set to Band 1. The RF signal is passed from the
??? plate of V1 through R4 and down to R26/C29. It cannot appear below
that
??? RC combination because the B+ line should be at ground for RF. So
??? without C62, there is no path for RF forward from V1, at least in the
??? schematic.

??? So I wonder whether Emanuele might achieve good results across the
full
??? ranges of Bands 1 and 2 by adjusting the amount of capacitance his
??? gimmick provides or by using a 2.2 pF cap as in the S-40B.

??? 73,

??? Maynard
??? W6PAP


--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Very interesting Maynard. I am not sure I am seeing this straight
but it appears that there is an RC load on the RF tube coupled via the
2.2 uF cap to the tuned circuit of the mixer grid. Should result in a
fairly low gain and fairly broad tuning. That might be desirable for the
broadcast band I am still not sure how the antenna coupling works for a
balanced input.

On 2/14/2025 6:45 PM, Maynard Wright via groups.io wrote:

Hi, Richard,

You are right about the two small caps. But trace carefully what S1B
(front) is doing when set to Band 1. The RF signal is passed from the
plate of V1 through R4 and down to R26/C29. It cannot appear below that
RC combination because the B+ line should be at ground for RF. So
without C62, there is no path for RF forward from V1, at least in the
schematic.

So I wonder whether Emanuele might achieve good results across the full
ranges of Bands 1 and 2 by adjusting the amount of capacitance his
gimmick provides or by using a 2.2 pF cap as in the S-40B.

73,

Maynard
W6PAP


--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Hi, Richard,

You are right about the two small caps. But trace carefully what S1B
(front) is doing when set to Band 1. The RF signal is passed from the
plate of V1 through R4 and down to R26/C29. It cannot appear below that
RC combination because the B+ line should be at ground for RF. So
without C62, there is no path for RF forward from V1, at least in the
schematic.

So I wonder whether Emanuele might achieve good results across the full
ranges of Bands 1 and 2 by adjusting the amount of capacitance his
gimmick provides or by using a 2.2 pF cap as in the S-40B.

73,

Maynard
W6PAP

C-62 in the S-40B is a small cap from the plate of the RF amp to
the grid of the converter. In the S-85 there are two such caps, one on
each of the low band tuned circuits. All listed as Bakelite caps. I have
seen illustrations of Bakelite caps somewhere, essentially a very low
value cap made by embedding two wires in a pit of Bakelite. Probably
more accurate and stable than a gimmick. I am no longer certain I can
analyze this circuit but it appears that these small value caps are to
equalize the gain of the RF stage.
I wonder if there was ever a Sam's or Rider's handbook for the S-85
or the S-40B for that matter. Both seem to have redrawn factory
schematics and are often somewhat clearer. I looked but could not find any.
I looked at the photo of the bottom of the S-40B in the handbook
but its not really that clear. My idea was to see of the L-3 coil, which
is for both low bands, was situated such that it could be coupled by
mutual inductance to the other coils.
I also looked at the Radiotron Designer's Handbook to see if there
was anything in it about RF amplifiers. There is but it wasn't helpful.
I have some other material on broadcast receiver design and will keep
looking.
Its too bad that someone with a _working_ S-85 can't look at it and
seen what it actually there. Very frustrating.

On 2/14/2025 3:07 PM, Emanuele Girlando via groups.io wrote:

D

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

?