Ok, tried two different 6V6’s, no change. ? On the plates of the 6V6’s there is 6.8Vrms of 120hz ripple. If I remove the 6v6’s it drops to 4.7Vrms and the hum is no longer audible (as expected). ? With the 6V6’s back in (Russian tubes BTW), switching the bass “IN”, which shorts CH2 and C43, the hum goes away but has no impact on the measured ripple. ? These measurements are made with my o’scope. ? I did some poking through my “inventory” of parts and do not have a suitable choke to swap in for CH2 – still thinking there may be some leakage going on there……? ? Fun stuff huh? ? Tom W3TA ?
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From: [email protected] <[email protected]> On Behalf Of don Root
Sent: Saturday, February 15, 2025 6:19 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-28A Hum? Hi Jacques, I just received 1.5 cents from you. Your proposal may well be, but how do you explain the difference ?the switch setting makes? ? My two cents: If the 120Hz “hum” is still heard when the 6SC7 tube is removed, that could be that the output stage is not balanced current wise. Meaning: if one of the 6V6 is way less polarized (more weak) than the other, that could be the cause. ? 73, Jacques, VE2JFE in Montreal ?
--
don??? va3drl
|
I have not read all the posts on this thread so may be repeating
something. Tom, I do not have an SX-28, In normal operation what does
the bass switch do? Does the bass increase or decrease when the switch
is in the IN position? The handbook is confusing. The schematic suggests
the BASS switch boosts the bass by adding a resonant choke on the output
of the first audio amplifier. The schematic shows the switch cutting off
the choke in ON, that looks backward to me. The additional TONE control
is just a conventional high roll off. It appears that both of these tone
controls are independent, is that correct.
It seems to me the bass boost should INCREASE hum.
The plate transformer of the output stage connects to the input of
the B+ filter. This is not raw AC since there is a fairly large cap
across it. The balanced circuit should remove any residual hum. The
rest of the amplifier is fed by filtered B+ and seems unlikely to have
significant hum on it. Try shorting out the tone control choke, if its
getting induced hum that should eliminate it.
Since you practically rebuilt the receiver perhaps some wiring
error was made or some new part is actually bad. Worth going over again.
It is always frustrating to me to try to trouble shoot problems
where I can't just jump in an make measurements.
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On 2/13/2025 4:21 PM, thoyer via groups.io wrote: I just finished pretty much a complete overhaul of a nice condition
(physically) SX-28A. Replaced just about every resistor and all caps.
Radio is working well except for a 120hz hum. When I switch the Bass in,
the hum goes away.
Yes, there is ripple on the plates of the 6V6’s, about 6vrms, but that
is there independent of the bass switch position. The output side of the
HV filter is clean, no ripple. I paralleled another 47uf 450v cap across
the choke input cap and there was no difference.
I double checked the wiring against the schematic along with component
values. Is the schematic correct in this area? I found once schematic
error maybe there is another?
Thoughts?
Tom
W3TA
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
We were writing at the same time and obviously (good word) have the
same questions.
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On 2/15/2025 3:34 PM, don Root wrote: Maynard ??re ????“ _So, in the S-85 schematic there is no coupling at
all from the plate of V1 to the grid of V2_.”
Well??? ?Maybe_So, in the S-85 schematic there is no _*_obvious_*_
?coupling at all from the plate of ?V1 to the grid of V2_. as the
receiver works on the Upper parts of the band. I understood this, but
peekers-in might not, and we have been all over the map on this… ?well
he is in Italy I think.
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
This is getting difficult to talk about. The antenna stage, i.e. the circuit between the antenna and the RF grid, is virtually the same in both receivers. The plate circuit is not the same. In the S-85 the broadcast band (540 to 1600) is not the same. In the S-85 the plate load of the RF amplifier is an untuned 6800 ohm resistor R-29 and C-26, a 220uuf capacitor across it. This is capacitance coupled by C-10, to a tuned circuit in the grid of the mixer tube. The antenna tank and this tuned tank will have some selectivity but it will be lower than on the other bands. On the second band there is a 6800 ohm resistor acting as the plate load, also coupled to the grid of the mixer through C-10 with a tuned circuit in the grid. Without the 220uuf cap the gain should be higher. Both coils for the mixer grid seem to be wound on the same former with separate trimmers. The puzzler here is where is the ground return for the antenna stage of the two lower bands? On the two top bands the coils are link coupled with one side going to A2 and grounded through the link on the antenna termimals. On the two lower bands there does not seem to be any sort of ground return for an ballanced load. A2 does not go anywhere. True on both the S-40B and S-85. If a single wire antenna is used the return is via the ground terminal, A2 goes no where. Yet the receivers is specified as using either a single wire or balanced antenna on all bands. So how are the two grid coils on L3 connected for a balanced antenna? We have discussed all sorts of illusory connections but I still can't see how any of them work or how to prove that they work. My suggestion of connecting a signal generator or other source (a piece of wire) to A2 with A1 grounded is to see if there is any signal that way. Now, the original question was why do not the trimmers on the two lowest bands do anything? First of all, is this correct, do neither antenna or mixer trimmers work? Is it on both bands or only the antenna stage? I will find the original post and see what was asked. This may be a separate problem. Now, I don't want to go through the entire long thread again (but will despite being lazy) but have we heard from anyone with a working S-40B or S-85 about whether their trimmers work or whether their receivers have reasonable response on the two low bands? Hallicrafters made both receives for some time so they can't have been totally inoperative on even one band let alone two. The original poster (not sure of spelling Emmanuel?) seems to have an adequate signal generator. Could he try feeding a signal into the grid of the mixer tube or at the plate of the RF amplifier (using a blocking capacitor) to see if there is response at that point. If neither trimmer works its necessary to isolate where the problem is (could be both places). I have no definite suspicions at this point. The circuit is a puzzle because as its shown it appears that it can't work. We have been over the possibility that the schematic is wrong or that the receiver is wired wrong (would never have worked so how did is escape from the factory?) I still want to know what happens if a signal is injected into the A2 terminal with the A1 terminal shorted to ground. On 2/15/2025 3:03 PM, don Root wrote: Richard , I am getting confused. ?you spoke of the antenna stage,? I
don’t see ?difference you mentioned between the 40B and the 85.
The next wording must be part of the mixer tuning. On the bama drawing,
C10 is active only on band 4,? and does nothing when on band 1, all as
we have been mentioning. Can you send us a snip of your drawing, it
might have a magic answer.
RE _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_.?? ?I cant see that Richard, and we spoke of the ?C62 in
the S-40B as likely doing the coupling for Band 1,2
Back to the Antenna tanks for band 1,2 ; we think my proposal way back
[see the sketch] has the answer. Have a look and see if it is right or
wrong. We asked but you did not comment at the time.
Emanuele still has the original problem, and has done many tests
already, and published images, and still has that very poor sensitivity
on the lower half of both lower bands; very frustrating.
the tank peaking for bands 1,2 is way too far off so AFIK he is not
concerned about all the antenna variables you might run into.
Maybe you can review past postings, and highlight specific errors one by
one.
*From:*[email protected]
[mailto:[email protected]] *On Behalf Of *Richard Knoppow
via groups.io
*Sent:* Saturday, February 15, 2025 4:54 PM
*To:* [email protected]
*Subject:* Re: [HallicraftersRadios] S-85 refurbish: I've got a problem
during the RF alignment of bands 1 and 2 - trimcaps don't peak!
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. …. ++++++++++
+++++++
Richard Knoppow Los Angeles WB6KBL SKCC 19998
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Maynard ??re ????“ So, in the S-85 schematic there is no coupling at all from the plate of V1 to the grid of V2.” Well??? ?Maybe ?So, in the S-85 schematic there is no?? obvious? ?coupling at all from the plate of ?V1 to the grid of V2. ??as the receiver works on the Upper parts of the band. I understood this, but peekers-in might not, and we have been all over the map on this… ?well he is in Italy I think. -- don??? va3drl
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Greetings to the Group:
?
?? I tried to take some photos using my digital microscope, but unless you want a close-up of a rivet in the band switch, the magnification is too high and the field of view is too narrow.
?
?? I therefore took the best photos I could using my digital camera.?? I have annotated these to show component id's.?? They largely duplicate Emanuele's work but I will post them anyway in case someone is interested in the variations between receivers.?? I hope they are of some help.
?
73,
Jim T.
KB6GM
--
Jim T.
KB6GM
|
Hi Jacques, I just received 1.5 cents from you. Your proposal may well be, but how do you explain the difference ?the switch setting makes?
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From: [email protected] [mailto:[email protected]] On Behalf Of Jacques_VE2JFE via groups.io
Sent: Saturday, February 15, 2025 5:57 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-28A Hum? My two cents: If the 120Hz “hum” is still heard when the 6SC7 tube is removed, that could be that the output stage is not balanced current wise. Meaning: if one of the 6V6 is way less polarized (more weak) than the other, that could be the cause. ? 73, Jacques, VE2JFE in Montreal ? -- don??? va3drl
|
Tom I’m glad I have company on that. Because the switch makes the difference and is before the 6V6s, I tend to think it is up there. Perhaps put a sizable cap on each grid to see if the switch affects the hum. Do you have a scope? Nasty little problems keep us busy on the forum. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of thoyer via groups.io
Sent: Saturday, February 15, 2025 5:34 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-28A Hum? “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 -- don??? va3drl
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Richard , I am getting confused. ?you spoke of the antenna stage,? I don’t see ?difference you mentioned between the 40B and the 85. The next wording must be part of the mixer tuning. On the bama drawing, C10 is active only on band 4,? and does nothing when on band 1, all as we have been mentioning. Can you send us a snip of your drawing, it might have a magic answer. ? RE 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.?? ?I cant see that Richard, and we spoke of the ?C62 in the S-40B as likely doing the coupling for Band 1,2 Back to the Antenna tanks for band 1,2 ; we think my proposal way back [see the sketch] has the answer. Have a look and see if it is right or wrong. We asked but you did not comment at the time. ??? Emanuele still has the original problem, and has done many tests already, and published images, and still has that very poor sensitivity on the lower half of both lower bands; very frustrating. the tank peaking for bands 1,2 is way too far off so AFIK he is not concerned about all the antenna variables you might run into. Maybe you can review past postings, and highlight specific errors one by one. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Richard Knoppow via groups.io
Sent: Saturday, February 15, 2025 4:54 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!? 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. …. +++++++++++++++++
?
? -- don??? va3drl
|
My two cents: If the 120Hz “hum” is still heard when the 6SC7 tube is removed, that could be that the output stage is not balanced current wise. Meaning: if one of the 6V6 is way less polarized (more weak) than the other, that could be the cause. ? 73, Jacques, VE2JFE in Montreal
|
“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 ?
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From: [email protected] <[email protected]> On Behalf Of don Root
Sent: Saturday, February 15, 2025 5:14 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-28A Hum? 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. ? ? More likely that the filter inductor and the tone inductor are talking to each other.? I don't know exactly where they are located on the chassis but I have noticed that high power Peavey 8 ohm to 70 volt line transformers talk to each other when co-located.?? Lots of strange things happen when there is some corrosion between the mounting screw and the chassis.? Loss of a "common" connection or some weird ohmic connection plays havoc with any circuit.
--
don??? va3drl
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Hi, Richard,
The S-40B also has the same R26/C29 network that passes plate current
from V1. The significant difference between the schematics of the S-85
and the S-40B is that the S-85 has no C62.
So, in the S-85 schematic there is no coupling at all from the plate of
V1 to the grid of V2. Emanuele added a gimmick which improved signal
flow considerably. But I think he may need to "tune" its capacitance a
bit to bring things to a point where he can properly align the input
stages to the mixer. That's why I suggested looking at C38, to get an
idea of just "how much" gimmick he would need to replace the missing C62.
Note that on Band 1 C10 is not connected to anything in the signal path
in the S-85. S1B (front) and S1B (rear) leave that part of the circuit
completely disconnected on Band 1.
Antenna terminal A2 is completely disconnected from anything in my S-40B
according to the schematic and by my measurements on Bands 1 and 2, but
it wouldn't hurt to perform the test you suggest.
73,
Maynard
W6PAP
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On 2/15/25 13:54, Richard Knoppow via groups.io wrote: 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
|
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. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Saturday, February 15, 2025 1:29 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] SX-28A Hum? More likely that the filter inductor and the tone inductor are talking to each other.? I don't know exactly where they are located on the chassis but I have noticed that high power Peavey 8 ohm to 70 volt line transformers talk to each other when co-located.?? Lots of strange things happen when there is some corrosion between the mounting screw and the chassis.? Loss of a "common" connection or some weird ohmic connection plays havoc with any circuit. -- don??? va3drl
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
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.
toggle quoted message
Show quoted text
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
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
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
toggle quoted message
Show quoted text
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
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
I will have to look at both schematics again but think there is a
"gimmick" in one or both for coupling the BFO.
toggle quoted message
Show quoted text
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
|
Don More likely that the filter inductor and the tone inductor are talking to each other.? I don't know exactly where they are located on the chassis but I have noticed that high power Peavey 8 ohm to 70 volt line transformers talk to each other when co-located.??
Lots of strange things happen when there is some corrosion between the mounting screw and the chassis.? Loss of a "common" connection or some weird ohmic connection plays havoc with any circuit. Jim
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
Jim, it seems like switching makes the big difference. Presumably there are 3 longer wires running a distance to the switch. Might one of them be getting to close to the B+ wires, or something like that. Although It hardly matters, the switch is for base “boost” I think, but the boost seems to be bypassed while in the ‘IN” position, and in use while in the “out position”.. confusing to me so far. ??
--
don??? va3drl
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Maynard, if we shift to the S-40B for a second, I also was disturbed by C62 which would try to pass band 4 30MC signals, bypassing the tanks. My guess was that the tanks must overpower C62. Even if somebody had, a good modeling program, we don’t know anything about the L6 parameters, so calculations cant be done. As I said some time ago, the S-40A does not have that C62, and band 1 uses a transformer …etc so a mysterious ongoing design. ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Maynard Wright via groups.io
Sent: Saturday, February 15, 2025 12:36 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!? 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 -- don??? va3drl
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Maynard,? good to know that they show a gimmick like this 
But that leaves the that ongoing v1-v2 coupling question ?more mysterious. ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Maynard Wright via groups.io
Sent: Saturday, February 15, 2025 11:57 AM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!? 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 -- don??? va3drl
|
Re: S-85 refurbish: I've got a problem during the RF alignment of bands 1 and 2 - trimcaps don't peak!
Maynard,? FYI 
? -- don??? va3drl
|
don Root
Jacques_VE2JFE
Jim Whartenby