Yes, hum is present – at the same level – regardless of the AF gain position. It does not change with AF gain adjustment so the issue is after the AF gain pot.

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CH1 and CH2 are not near each other. CH2 is on the front of the chassis and CH1 is in the rear corner.

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Tom

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6SC7, sorry.

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Thanks for the input, yes more poking is needed. Hopefully later tody.

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Tom

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Richard, we agree about the switch position labels on the schematic being reversed.

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Hi Jacques, last reply tonight

Ok Ill try. I guess I must be getting cranky!

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I followed this case more or less since Emanuele posted it, so be kind if I misunderstood anything about.

I remember that Emanuele complained about a complete loss of sensitivity in the lower part of the Bands 1 and 2: is it right ? ???yes

Does somebody already asked him to check the amplitude of the Local Oscillator at the low end of those two bands ??? ??don’t think so

My doubt is: this seems to be an alignment problem, yes ?but what will be the effect of a “dying” LO on the low end of the BC band, for example ? I don’t know

That can happen if the Q of the oscillator coils is lower than they should be, or if the 6SA7 is end-of-life (not enough gain).

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FYI He said the LO aligned well on all bands, the RF and mixer tanks align and work well on band 3,4 ??but the RF and mixer tanks ?of 1,2 don’t align apparent too much mmFd at minimum.?? He has an impedance sweeper of some sort, and they show resonance too low, say 1200 kc not 1400 but don’t quote me.?

I was trying to get him ?to sweep at 600kc dial position, because if that if way off no little trimmer will help. Im sure he did a lot before posting and knows a lot.

I felt that it is a common mode problem ?all four tanks, but ?if so it has not been found. ???If the LO was weak, wouldn’t it show up first on band 4? … a question.

But your though may well be IT.? I don’t know how he did the sweeps but I would think they would be independent of the LO, mystery continues< I quit for now. Please fix my spellink ??I’m too tired.

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Bob, Some of us are not bean counters, but want to know now things work and don’t work, and give them some love too.

You can go back to Stephah Gray in about 1750 who found out electric fluid moves fast and far .. and early telegraphs ?ideas arose and later Cook, and Morse ones and Mr. Baudot’s codes and stuff, ?transatlantic cables.. they didn’t quit. remember Marconi; he didn’t quit.

If we were in business there would be ?huge piles behind our houses and we would be calling Chinese amazon every day for a new dog to throw into the pile.

I would never make a bench Technician, ?but I had to startup new steel mills, with germanium transistors and big SCRs and where the dogs had to be tamed and trained out in minus 40 weather…not a couchy bench job.

Some of us just don’t fit into todays business society….Missfits.

Bob, we have a bit of snow but if you are in Toledo, your gonna need a big scale to handle all the fluff Mississippi is sending up. The radar has all kinds of colours showing up. We are ducking up here. Good luck

Hi Don,

I followed this case more or less since Emanuele posted it, so be kind if I misunderstood anything about.

I remember that Emanuele complained about a complete loss of sensitivity in the lower part of the Bands 1 and 2: is it right ?

Does somebody already asked him to check the amplitude of the Local Oscillator at the low end of those two bands ?

My doubt is: this seems to be an alignment problem, but what will be the effect of a “dying” LO on the low end of the BC band, for example ?

That can happen if the Q of the oscillator coils is lower than they should be, or if the 6SA7 is end-of-life (not enough gain).

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Maynard , I’m gonna mess-up your fine writing! .. Sorry.

If there is stray coupling transferring signals at the top end of each
band, we might expect that it would see lower loss at the higher
frequencies, yes ?and that is what is happening, it seems. I’m on the fence ?And even though
there is signal flow at the high end of each band, it isn't very robust
if I recall the earlier messages correctly. I wonder, ?Emanuele was focused on alignment, and said the bottom end was very bad , and perhaps the top was useable, all as I recall, but can’t be accurate.

And we need to keep in mind that there may be two problems here and not
confuse them. Well Emanuele raised one problem, somebody else started into the other. ??

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Richard is thinking about the circuitry between the
antenna terminals and V1, the RF amp and quite appropriately so. Yes but that only matters is you add an external wire to A2 and remove the link ??

?I think that Hallicrafters changed the S-40A circuitry to eliminate one
coil in that part of the S-40B and it makes the circuitry in the
schematic look as if it is miswired but I don't think it is. Well Maynard, my speculation is that the 40A was not operating so well, possibly because the transformers had too much Q, but the various antennas swung the ?tunning off course, so they flattened the resonance .. all speculation because they kept mucking with band 1 and 2. ?We could start a conspiracy case!

To save that one coil, I think they gave up balanced inputs on Bands 1
and 2, but didn't revise the instructions in the manual to indicate that. Well, they don’t want to admit a problem

The other problem is with the tuned circuits between V1 and V2 and I
think that's where Emanuele's problem is.? It is a mystery to me so far, all I know is from what he said; all of the 4 tanks appear to need less capacitance when aligning, and the lower half of the bands are useless[my word]. ?Many many things have been checked and checked, yet nothing makes sense. BTW I watch “mayday” mostly about planes crashing, and long investigations to try to dig out the cause{s}. they try everything. ??

Thanks, Jim T., for the very nice pictures. Those are helpful and of
really good quality. Yes , very good of Jim ?to do all that work

Some thoughts:

1. I don't see any evidence of C62 or a gimmick in Jim T.'s receiver.
If it is working well without that coupling then my thoughts about this
are probably incorrect;? ?we will see

2. The S-85 and S-40B schematics seem to be identical in the circuitry
between V1 and V2. One of them must be incorrect for these various
circuits to work properly;? except for C62???

3. Someone might own and use an S-85 and, if they don't pay much
attention to the lower ends of Bands 1 and 2, they might have the same
difficulty as does Emanuele without observing it.? hard to believe,? but sometimes we buy stuff that works badly and are so disillusioned that it goes to the attic out of sight and some picker finds it 70 years later, and passes it around and around till it comes out here.


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--
don??? va3drl

Tom, as you are able to measure it, what is the ripple across C48 and across C44 when the bass switch is “IN” ?

What is not normal is to have more “hum” when the bass switch is “OUT” because the first triode section of the 6SC7 will have less gain in low frequencies (CH2 reactance will drop as the frequency lowers) and also at high frequencies (C43 reactance will drop).

The CH2 – C43 should be broadly resonant around 1kHz or so…

But if there is a 120Hz component present across C44, it will be coupled to the V14 grid thru C45 and also to V13, inverted in phase due to the see-saw phase splitter circuit driving the second 6SC7 grid (pin 3).

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The whole situation reminds me of a restoration report about a SX-28A that I read sometime ago, in which the C48 was found almost “open” (less than 1?F in value).

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It seems that the way to look at this switch is that in one position the plate load is provided by the choke while in the other the load is switched to R37, and as an aside the choke gets shorted ? ??Any votes on this? ?just for fun try the thumbs ?voting machine, I won’t look.

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Maynard , I’m gonna mess-up your fine writing! .. Sorry.

If there is stray coupling transferring signals at the top end of each
band, we might expect that it would see lower loss at the higher
frequencies, yes ?and that is what is happening, it seems. I’m on the fence ?And even though
there is signal flow at the high end of each band, it isn't very robust
if I recall the earlier messages correctly. I wonder, ?Emanuele was focused on alignment, and said the bottom end was very bad , and perhaps the top was useable, all as I recall, but can’t be accurate.

And we need to keep in mind that there may be two problems here and not
confuse them. Well Emanuele raised one problem, somebody else started into the other. ??

?

Richard is thinking about the circuitry between the
antenna terminals and V1, the RF amp and quite appropriately so. Yes but that only matters is you add an external wire to A2 and remove the link ??

?I think that Hallicrafters changed the S-40A circuitry to eliminate one
coil in that part of the S-40B and it makes the circuitry in the
schematic look as if it is miswired but I don't think it is. Well Maynard, my speculation is that the 40A was not operating so well, possibly because the transformers had too much Q, but the various antennas swung the ?tunning off course, so they flattened the resonance .. all speculation because they kept mucking with band 1 and 2. ?We could start a conspiracy case!

To save that one coil, I think they gave up balanced inputs on Bands 1
and 2, but didn't revise the instructions in the manual to indicate that. Well, they don’t want to admit a problem

The other problem is with the tuned circuits between V1 and V2 and I
think that's where Emanuele's problem is.? It is a mystery to me so far, all I know is from what he said; all of the 4 tanks appear to need less capacitance when aligning, and the lower half of the bands are useless[my word]. ?Many many things have been checked and checked, yet nothing makes sense. BTW I watch “mayday” mostly about planes crashing, and long investigations to try to dig out the cause{s}. they try everything. ??

Thanks, Jim T., for the very nice pictures. Those are helpful and of
really good quality. Yes , very good of Jim ?to do all that work

Some thoughts:

1. I don't see any evidence of C62 or a gimmick in Jim T.'s receiver.
If it is working well without that coupling then my thoughts about this
are probably incorrect;? ?we will see

2. The S-85 and S-40B schematics seem to be identical in the circuitry
between V1 and V2. One of them must be incorrect for these various
circuits to work properly;? except for C62???

3. Someone might own and use an S-85 and, if they don't pay much
attention to the lower ends of Bands 1 and 2, they might have the same
difficulty as does Emanuele without observing it.? hard to believe,? but sometimes we buy stuff that works badly and are so disillusioned that it goes to the attic out of sight and some picker finds it 70 years later, and passes it around and around till it comes out here.


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Richard,

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When the bass switch is “in” it boosts the bass. Going by the schematic it shows that it shorts the choke / cap. Audibly it definitely boosts the bass, I need to confirm the wiring of the switch vs the schematic. Wouldn’t be the first error I’ve found.

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Yes, the tone adj and the bass boost are independent.

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You suggested shorting the choke – but isn’t that effectively what the switch is doing?

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And I agree, I had most of this radio torn apart so it is a good possibility there is a miswire somewhere in that circuit – wouldn’t be the first time………..

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Thanks,

Tom

W3TA

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I unscrewed CH2 from the chassis and let it float, no change.

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Richard, yes it is hard to describe what is actually a drawing on paper.? Perhaps you don’t have anything to copy what you see.

Here, I am using ?

and see ???this

As I see it , C10 is only used in band 4 ?

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This is getting difficult to talk about. Yes ?The antenna stage, i.e. the
circuit between the antenna and the RF grid, is virtually the same in
both receivers. Yes [S-85 ?and S-40B {reference} ] ??The plate circuit is not the same. Yes?? ?

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In the S-85 the
broadcast band (540 to 1600) is not the same. Yes ?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. Yes? ???This is capacitance coupled by C-10, to a
tuned circuit in the grid of the mixer tube. No ?look at image.

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The antenna tank and this
tuned tank will have some selectivity but it will be lower than on the
other bands. ??

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On the second band there is a 6800 ohm resistor acting as
the plate load, Yes ?also coupled to the grid of the mixer through C-10 No with
a tuned circuit in the grid. ???No, I see a 6800 ohm resistor ?running to band 3 coil L5 ?but there is no ?OBVIOUS path to the grid cct WHEN ON BAND 2; ?admittedly a very strange dangling signal raising all kinds of questions????????? Without the 220uuf cap the gain should be higher. ??, ????????Both coils for the mixer grid [L6] seem to be wound on the same ?former with separate trimmers. Yes? ???

The puzzler here [we are trying to solve the band 2 mixer dilemma ]? 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.

I [we] have seen no answer and ?gave up long ago and resorted to a long wire and the link closed to solve Emanuele’s problem ??

Now, the original question was why do not the trimmers on the two
lowest bands do anything? Not accurate, read again from the start.. all words matter. 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. You need to read all his posts again, if you want to understand the situation.
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? read all ?posts again ?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. read all his posts again as he has done equivalent tests I think
If neither trimmer works its necessary to isolate where the problem
is (could be both places). read all his posts again
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?) ?it is always possible on friday 5 PM before Christmas and the boss says “meet the quota for the year”???????

?I still want to know what happens if a signal is injected into the A2 terminal with the A1 terminal shorted to ground. ?Wait your turn Richard, don’t get pushy, he has to go to work {big smiley thing|.

You can ask all the questions you want, but like the lawyers, you need to know the answers yourself. or

?Questions ?are cheap, ?the answers is ?“don’t ask me”

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