Hi all: I am back with a question on a discriminator
i.f replacement for a stromberg 350-m . I searched as recommended by CV here on the site for a couple of chassis to pull one from . Did not come across one yet but will keep looking until the day one comes my way.In the mean time I have a Miller 12-c45 455khz
i.f discriminator which has a 30 khz peak seperation and 17 khz linearity .I am thinking this will work in this 2nd i.f can that drives the Oscillator freq for the A.F.C control . But I do not know . I am guessing
and do not know exactly what I am replacing because the only spec is the part number.Which goes against all my senses . So my question is ...Is this a correct replacement or close enough? Or not close at all? I am thinking this would at least have a chance of working based on what I was told by CV.I did read up on discriminators which helped . But no discription on the print other than part number makes it tough to know what to sub if anything .I am still just getting started on this ,mostly doing the cabinet now .Thanks!
bill

:Hi all: I am back with a question on a discriminator
:i.f replacement for a stromberg 350-m . I searched as recommended by CV here on the site for a couple of chassis to pull one from . Did not come across one yet but will keep looking until the day one comes my way.In the mean time I have a Miller 12-c45 455khz
:i.f discriminator which has a 30 khz peak seperation and 17 khz linearity .I am thinking this will work in this 2nd i.f can that drives the Oscillator freq for the A.F.C control . But I do not know . I am guessing
:and do not know exactly what I am replacing because the only spec is the part number.Which goes against all my senses . So my question is ...Is this a correct replacement or close enough? Or not close at all? I am thinking this would at least have a chance of working based on what I was told by CV.I did read up on discriminators which helped . But no discription on the print other than part number makes it tough to know what to sub if anything .I am still just getting started on this ,mostly doing the cabinet now .Thanks!
:bill
:
Hi Bill,
I have encountered discriminators whose center frequency was 8.3MHs up to the common 10.7MHz, but never at 455KHz.
Did I get something wrong?

Best regards,

Bill Grimm

::Hi all: I am back with a question on a discriminator
::i.f replacement for a stromberg 350-m . I searched as recommended by CV here on the site for a couple of chassis to pull one from . Did not come across one yet but will keep looking until the day one comes my way.In the mean time I have a Miller 12-c45 455khz
::i.f discriminator which has a 30 khz peak seperation and 17 khz linearity .I am thinking this will work in this 2nd i.f can that drives the Oscillator freq for the A.F.C control . But I do not know . I am guessing
::and do not know exactly what I am replacing because the only spec is the part number.Which goes against all my senses . So my question is ...Is this a correct replacement or close enough? Or not close at all? I am thinking this would at least have a chance of working based on what I was told by CV.I did read up on discriminators which helped . But no discription on the print other than part number makes it tough to know what to sub if anything .I am still just getting started on this ,mostly doing the cabinet now .Thanks!
::bill
::
:Hi Bill,
: I have encountered discriminators whose center frequency was 8.3MHs up to the common 10.7MHz, but never at 455KHz.
: Did I get something wrong?
:
:Best regards,
:
:Bill Grimm
:
Bill: Well those would be normal I guess.What you might see in an FM circuit I think . And I am not an
expert there either . But this is an odd ball used to
tune in the strongest station on am band push button
tuning . It does that (if i understand correctly) by shifting the oscillator frequency slightly until the center frequency and therefore the closest channel is balanced out in a sort of feedback loop .Hence the window 35khz and 17 khz linearity spec. Of course I have low confidence in my knowledge on this and I am open to being wrong . But that is how i see it currently . I would'nt even have to know how it worked if there were any specs on it and I could find a similar part. So I am throwing it out here due to my lack of certainty . Short answer is i think it is 455 khz center becuase it is AM
bill

Hi Bill,
Give me a dope slap. In 1939 I don't think FM45 was around yet. This set has a lot of interesting circuitry in it. I took it for a set that would tune the FM45. It looks like it doesn't
It looks like they hired Armstrong to design exotic circuitry to keep their push buttons on tune. The result is a highly challenging radio.

Best regards,

Bill Grimm

:Hi Bill,
: Give me a dope slap. In 1939 I don't think FM45 was around yet. This set has a lot of interesting circuitry in it. I took it for a set that would tune the FM45. It looks like it doesn't
: It looks like they hired Armstrong to design exotic circuitry to keep their push buttons on tune. The result is a highly challenging radio.
:
:Best regards,
:
:Bill Grimm
:
Bill: I just read your reply here and I like your assessment! It's like they had spare parts and decided to use them.I know from reading here you have more experience on these things than I do . So I am really lost on it ! As I recap it I change my view of the circuit daily . Most of the challenge is now on L21 .
My latest view is that this with R16 and c44 is a low pass filter and L21 is just an inductor . Using a online calculator I figured for LCR low pass filter. And come up with a .0004 henry coil would giving a cutoff frequency of 24khz.Passing the audio spectrum onward .Blocking higher freq. Ask me tomorrow and I'll tell you a completely different story . In the mean time I will keep and eye out for an original part. And just solder it in !If I get everything else done before that I will get some spare parts and the scope fired up .

Best Regards;
bill

::Hi all: I am back with a question on a discriminator
::i.f replacement for a stromberg 350-m . I searched as recommended by CV here on the site for a couple of chassis to pull one from . Did not come across one yet but will keep looking until the day one comes my way.In the mean time I have a Miller 12-c45 455khz
::i.f discriminator which has a 30 khz peak seperation and 17 khz linearity .I am thinking this will work in this 2nd i.f can that drives the Oscillator freq for the A.F.C control . But I do not know . I am guessing
::and do not know exactly what I am replacing because the only spec is the part number.Which goes against all my senses . So my question is ...Is this a correct replacement or close enough? Or not close at all? I am thinking this would at least have a chance of working based on what I was told by CV.I did read up on discriminators which helped . But no discription on the print other than part number makes it tough to know what to sub if anything .I am still just getting started on this ,mostly doing the cabinet now .Thanks!
::bill
::
:Hi Bill,
: I have encountered discriminators whose center frequency was 8.3MHs up to the common 10.7MHz, but never at 455KHz.
: Did I get something wrong?
:
:Best regards,
:
:Bill Grimm
:
Bill Let me add this is a 1938 set.It does'nt have the kind of push button coils and adjustments you see on say a 1940's Philco . Which I think must have put this design to bed!Or was supposed to improve that type of circuit?It's a different approach for sure! I think I have saved about thirty radios to date but never ran across this.I am kind of curious to see what it does!
bill

I think that unless you are prepared to do a lot of experimental fiddling, it is going to be very difficult to salvage the AFC operation on this set. Main reason being the L21 winding and its physical relationship being unknown (without having an actual part to go by) to the other parts of the second IF coil, since as you explained in a previous post the set was missing this transformer when you acquired it.

However, you should be able to cobble in a standard 455 kHz IF coil (without the center tap and L21 coil) so that you can couple over and demodulate the IF signal without having the AFC function. This will require rewiring of the 6H6 dual rectifier tube (only one side would be required). This will allow you to get the radio playing, but without the AFC fine tuning feature for the pushbuttons.

Lack of fine tuning on pushbuttons may or may not be a problem. It is definitely needed on my 1937 Grunow 1291, which has mechanical pushbutton tuning with AFC auto-fine-tuning to "take up the slop"; but my 1937 RCA 811K, which uses an electromechanical pushbutton tuning scheme, seems to be repeatable enough that the AFC feature isn't really needed (although it has it). And, my 1948 Scott 800-B uses a pushbutton tuning scheme (motorized disk) that is similar in concept to that of the 811K, but it has no AFC at all and apparently doesn't need it on AM (although it would be very nice to have on the FM band due to warmup drift).

Another AFC set that I own is a 1937 Motorola 10Y-1. This uses a very sloppy friction-drive-motor scheme to crank the tuning cap around in response to a pushbutton selection. AFC is a necessity in this set due to the imprecision of the tuning drive.

So, depending how "repeatable" your mechanical pushbutton-selection scheme is, AFC might not be a great loss. Worst case scenario would be that you would have to manually fine tune the set after you used a pushbutton to select a station. Since this is AM (relatively low frequency) it should be drift-free once tuned, even without AFC.

Your best bet to get this set working as it left the factory might be to acquire an identical junk chassis with the 2nd IF transformer intact.

You might take a look at the Stromberg-Carlson Model 345-M schematic. This radio appears to be very similar to the Model 350-M, but doesn't have AFC. This info might facilitate converting your set to non-AFC operation, if that should be necessary.

:You might take a look at the Stromberg-Carlson Model 345-M schematic. This radio appears to be very similar to the Model 350-M, but doesn't have AFC. This info might facilitate converting your set to non-AFC operation, if that should be necessary.
:
CV Thanks again for response as well to Bill Grimm .
It is odd that I am trying to get this to work in the first place. Once it does I most likely won't even use it ! Still somehow it is interesting I guess. I will continue to look for a direct replacement as that is the best way to get there with out question .And maybe as you said the results will be less than spectacular . The set is already wired to work with out this circuit as you described .Appears to be done by a Philco repairman back in the 60's.

Back to the circuit .I am not sure if the placement of L21 on the core would be a problem . It (L21)should be at half the primary voltage. It along with RC componets between it and ground would control how fast the frequency difference from the center frequency would be controlled .And the output voltage to the oscillator grid varied .I could see what your are saying is true still . If the gain of the loop and
or the time of the response is to fast the loop and the control would not settle .Since L21 is a choke whose reactance depends on it's coupling to the primary I guess that could be a problem.Impacting both the gain and time response .I guess I am thinking out loud that you would be right on the position of the L21 coil. I am further guessing that this would only be a problem if it increased the response time of the loop or increased the gain so it could not settle?
So how different this is physically from the original would determine much.You have reactance from L21 current and mutual inductance from the primary .
That's a big question to quess at. I was hoping some how this would be relative to the spec's I stated above . But did'nt think about reactance which is not stated .
Without beating it up to much .It does sound like I could try it ? And then pull my hair out after!But I am also holding out that someone will have a Miller
12-c45 in a Stromberg Carlson 350-m . Yeah right !
Anyway thanks again for the info !!!
I think this will be a nice radio even without the AFC
if it comes to that .
bill

:You might take a look at the Stromberg-Carlson Model 345-M schematic. This radio appears to be very similar to the Model 350-M, but doesn't have AFC. This info might facilitate converting your set to non-AFC operation, if that should be necessary.
:

CV ,All: After checking better the can I do have miller(12-c45)does'nt even have the choke L21 .Wonder if it is still possible to use ? I am thinking L21 is not coupled to the primary and is strictly a choke .
bill

:You might take a look at the Stromberg-Carlson Model 345-M schematic. This radio appears to be very similar to the Model 350-M, but doesn't have AFC. This info might facilitate converting your set to non-AFC operation, if that should be necessary.
:

CV ,All: After checking better the can I do have miller(12-c45)does'nt even have the choke L21 .Wonder if it is still possible to use ? I am thinking L21 is not coupled to the primary and is strictly a choke .
bill

Don't know- L21 is inside the IF can but exactly how- if at all- it interacts with the pri/sec coils isn't obvious to me. If it's just a choke, I don't know why it would be inside the transformer can, except possibly for convenience.

:Don't know- L21 is inside the IF can but exactly how- if at all- it interacts with the pri/sec coils isn't obvious to me. If it's just a choke, I don't know why it would be inside the transformer can, except possibly for convenience.
:
CV : I think that is why . It is described as the return path for the diodes and also in parallel with the primary in the Navy "neets" manual I googled . Also described as a choke .Hard to relate that typical circuit to the tube circuit here.I will have to redraw the tube circuit it to make it clear. At a glance I would say there is some difference as the L21 coil returns to the center tap of the transformer in the typical circuit.And here it appears off one diode and not returning to the center tap as in the typical circuit.It actually appears to me that the diode in the 6B8 tube is the second diode of the discriminator.And not the second half of the 6h6.
I have to connect the chassis points on paper to visualize it as all those gorunds would be shown as wire in the typical circuit.Which may be why it looks so different .I admit I am at a point of confusion on it all.
Fact is this coil L21 probably should be there for it to work correctly.And there's nothing like the original.I will bet as you said before that is where I end up.Or a bunch of fiddling around will be needed.Then I will find an original and get it right !I am already thinking this coil would be identical to the primary.But it could be anything.If I finally find an original I'll post a photo of how it is wrapped.With out that original part everything is a guess!Good mental exercise. Thanks again for your help and replies!
bill