Hi: Irecently bought a 350-m console which is electrically close if not exactly the same as the curved front R version of this console .It was beat ,so I am just starting to strip and refinish . I ordered a print that hopefully is a little clearer than the free one here.Not complain there,but need a parts list also .
When I removed the chassis I noticed that the second if can was a miniature thumb sized generic if can 455khz. Instead of the large original with primary and discriminator adjustment.I plan on taking my time and getting this set right as it is nice. I am not sure I understand the circuit .But at a glance there is no center tap on the new can and the wire from it to the 6h6 cathode ( I believe )is therefore disconnected. Now the question .Does anyone know of a replacement for this? Or who made these(RCA?).I am kind of dead in the water here hoping that the new print will clue me in . By the way the replaced if Can was a repair from a shop back in the 60's.I did not try the radio (speaker is good).Appears this
circuit does some control of the oscillator . Fancy high fi stuff? Anyway I am stuck going forward.Eventhough I am striping the cabinet and not really working on the chasiss , this bugs me . If I can get a cross referenced or replacement from play things of the past or elsewhere that would be great.
But don't know much about the part.And the original
is gone .I am not sure how this replacement sets back the preformance becuase I do not know enough about the circuit. Maybe I can pick something close (if that is possible)? I know that I am not leaving it this way when I get to work on it.So any information would be appreciated.Even a basic idea of whats is going on with the circuit .Thanks for any help !!!
bill

The discriminator transformer is part of an AFC circuit that was necessary because of the way automatic tuning was implemented in this set: it is variable enough to be unreliable without AFC to "fine tune" the setting.

Basically, with the set in "Electric" tuning mode, selecting a station pushbutton will get you close to the preset station, then AFC will tune it the rest of the way. It does this by means of a feedback loop that continuously samples IF signal strength and directs the oscillator control to "pull" the local oscillator signal either high or low, in the direction that gives the greatest output.

The set will still work fine with AFC inoperable, although the tuning presets may be too imprecise to be usable. It's lso possible that they will work fine- the AFC circuit may have been "design overkill" for this application. (Stromberg-Carlson was noted for "never using two bolts when twelve would do.") Probably why they went out of the radio business. Grunow 1291 and RCA 811K/813K/816K sets used a similar AFC circuit and you may be able to locate a junk chassis of these from which you can harvest the necessary differential coil. These show up on eBay fairly regularly. Be aware that this coil is frequently found to be bad in Grunow sets, however.

:The discriminator transformer is part of an AFC circuit that was necessary because of the way automatic tuning was implemented in this set: it is variable enough to be unreliable without AFC to "fine tune" the setting.
:
:Basically, with the set in "Electric" tuning mode, selecting a station pushbutton will get you close to the preset station, then AFC will tune it the rest of the way. It does this by means of a feedback loop that continuously samples IF signal strength and directs the oscillator control to "pull" the local oscillator signal either high or low, in the direction that gives the greatest output.
:
:The set will still work fine with AFC inoperable, although the tuning presets may be too imprecise to be usable. It's lso possible that they will work fine- the AFC circuit may have been "design overkill" for this application. (Stromberg-Carlson was noted for "never using two bolts when twelve would do.") Probably why they went out of the radio business. Grunow 1291 and RCA 811K/813K/816K sets used a similar AFC circuit and you may be able to locate a junk chassis of these from which you can harvest the necessary differential coil. These show up on eBay fairly regularly. Be aware that this coil is frequently found to be bad in Grunow sets, however.
:
CV: That is good news to me! I never heard of that type of control to chase a station down. I guess someone must have got sick of readjusting those coils and tried this fix. I generally tune them in but do not use them much myself. It would be interesting to see how good or if this actually works . But I am happy with looking for the part in the places you suggested . It looks to be differential because of the connection to both the primary and secondary ?I noticed you used differential to discribe the coil. Must have been a hard coil to find quickly
back when it was repaired ( by a Philco repair shop) .
Or the owners did not like the button tuning either .
At any rate the new owner feels better about the situation. So thanks for all the information and help on this !!!
bill

Google "foster-seeley discriminator" and check out the Wikipedia entry. This has a better explanation of how the circuit works.

:Google "foster-seeley discriminator" and check out the Wikipedia entry. This has a better explanation of how the circuit works.
:
CV: Thanks for the link to this.That is a good discription and explains that center connection .
A bridge!That makes perfect sense.Did'nt strike me as a bridge though . I have to go look a an Fm circiut discriminator now .Anyway it is nice to have some idea how stuff works and to actually learn something instead of just replacing caps.I looked at the Rca circuit breifly and found they use two cans.But it looks very similar just broken into two parts.I see people tend to turn this feature off on their radios. And I may end up there myself . But I will get it working one way or the other anyway . I have other radios to listen to so I intend on taking time on this one . I'm going to dig into it .I like the idea behind it ,so I am still curious to see it work . Thanks again for the info!!!
bill