The Statesman (202-T) Wide-Band AM-FM Multiplex Tuner Preamp

Discussion in 'Fisher' started by dcgillespie, Jul 21, 2017.

  1. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Gadget -- The Custom Electra tuner/preamps in fact use a very large pulley on the tuning cap to achieve what you're talking about. The RF assemblies in the stand alone tuners usually use a gear reduction mechanism inside the RF box. I've determined however that I really jumped the gun with my comment, and could really take it out of the thread. I've compared the tuning of this unit now with that of an FM-100B, 200B, and my R-200, and completely withdraw the original comment. I should have checked it further before making it.

    Vendo -- The >30000 serial number units are by far the most desirable units to have, as in those units, Fisher got the signal path correct regarding the Tape Monitor switch, Tape Recording jack, and the Stereo/Mono Mode switch. In earlier units like mine, the signal goes to the Tape Monitor and Tape Recording jack first, and then to the Mode switch -- which (for example) screws things up if you want to have the AM tuner signal appear at both Recording output jacks. Later units (>30000) have the signal go to the Mode switch first, which corrects the problem. I've corrected the issue in my unit, but with how dense the wiring is, it ain't an easy job! Not to do neatly anyway. There were other changes made too, but this was probably the biggest one.......

    Dave
     
  2. Leland47

    Leland47 AK Subscriber Subscriber

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    Hi Dave.

    Would these upgrade/rebuild actions be basically the same to take on a Fisher 100-T Coronet ? (and)

    Is the selection of a Fisher WX sub chassis MPX recommended for the 100-T upgrade/rebuild also....or is a MPX 65 suitable for the job?
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Hi Leland -- You would definitely want to use a WX sub-chassis (or at least design), as it was designed to operate at the voltage levels that are present in a tuner only environment. The MPX-65 was an off-shoot of the WX chassis, designed to implement the basic Fisher multiplex sub-chassis into a receiver environment (where higher voltages exists) as economically as possible. As such, it is generally the more available sub-chassis, since Fisher sold sooo many receivers once that became their focus of direction. The good news is that for the purposes of retrofitting these tuner/preamps to the GE/Zenith format, the MPX-65 can be converted to the WX circuit easily enough by the change of one plate resistor, two tubes, and altering the indicator output circuit to that used by the WX design. There were other slight differences, but they are insignificant relative to the changes needed for use in these units.

    I will look to see if I can find a schematic of the Coronet/100-T. However, I am rather certain that replacement of the Ratio Detector transformer and the mono de-emphasis network would be required if you want maximum MPX performance, but the need for the control relays and how they might be connected into the circuit would just be a wild guess at this point. The need for the Audio Control relay in the Statesman/202-T is directly due to the makeup of the Input Selector switch used in that unit. Without knowing the makeup of that switch in the Coronet/100-T, any answer at this point would be pure speculation. A more sure bet is the need for the Eye Tube Control relay. Fisher didn't provide any means for indication of Stereo MPX reception in the Statesman/202-T, so it's a pretty sure bet that none was provided in the Coronet/100-T, either. Fisher just wasn't in that mode of thinking when these two models came out. In any event, if you are looking to have the FM eye tube react as Fisher ultimately engineered them to do in the GE/Zenith based units that used eye tubes, then the need for an Eye Tube Control relay is pretty much a sure thing.

    While I'm sure that implementing the outcome of the Statesman/202-T Wide-Band MPX project into a Coronet/100-T would have its differences, the overall approach would be much the same in implementing it. You would need to gather the necessary Ratio Detector transformer and MPX sub-chassis (don't forget the small RF choke that goes with the later RD transformer) from suitable sources/donors, study the design of the Coronet/100-T to see how to best implement a WX type chassis into that unit with the desired features/outcome, restore/modify/test/align the MPX sub-chassis as necessary, implement it into the unit, and test to ensure the final outcome is achieved. You would also need to have access to the necessary test equipment or someone knowledgeable with it to install the RD transformer and check the performance of the WX sub-chassis as well. I mention these things only because over the years, I have seen a number of these Crosby based Fisher units, where somebody just slapped an MPX-65 sub-chassis into it with little attention given to the detail differences between the two multiplex formats, only to have it either not work at all, or work so poorly as to effectively not work at all. With attention to the details however, I have no doubt that the Coronet/100T could also become a superb member of the Fisher Wide-Band MPX club, with all the Stereo MPX performance that Fisher was know for.

    Dave
     
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  4. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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  5. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Thanks so much Larry! I couldn't get the bottom link to work, but at the site I could retrieve it just fine.

    Dave
     
  6. Leland47

    Leland47 AK Subscriber Subscriber

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    Thanks Dave. The work needed as you laid out...is out of my league...but good to know the extent...and that it is possible!

    I love to listen to FM, but my main interest is having a Fisher tube Preamp! With models like the Fisher 400CX preamp bringing 4 grand....I thought the 100-T and now the 202-T would be very doable in comparison.

    Bringing them up to Fisher FM Broad Band standards of the later models is great!

    Please don't go out of your way ( on my account ) to delve into my 100T upgrade. But if you need any pics of my unit....or any sort of info I could get from the unit...I'd be glad to do so.

    I'll be looking around for a WX sub chassis....and saving my pennies. You might get a PM from me, in the next month or so...as I'd like to discuss getting the work done right.
     
    Last edited: Jul 24, 2017
  7. gadget73

    gadget73 junk junkie Subscriber

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    Pretty much why I have a Pilot tuner/preamp and not a Pilot preamp. The one I have was offered to me for an extremely modest price, and even the normal sell price is pretty reasonable compared to the preamp-only. Circuit wise its virtually the same, plus I get a tuner out of the deal.
     
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  8. vendo81

    vendo81 AK Subscriber Subscriber

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    I have a Fisher 100T. My tech put a modified MX65 into it for stereo reception. He did have to add some sort of relay/relays though but it works great. I'm sure it was modified to work like a WX chassis as Dave mentioned.


    Fisher 100-T.jpg Fisher 100-T 2.jpg
     
    Last edited: Jul 25, 2017
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  9. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    I just checked my FM-200 tuner, which was one of only two tuners that Fisher made with the "three groove" faceplate and no onboard MPX adapter (nor a place to install one). It has a ZZ592-170C transformer. I really need to find a schematic for that unit to see what might need to be adjusted for optimal GE/Zenith MPX performance.
     
  10. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Vendo -- Thanks for the pics -- and what a sharp looking 100-T!

    One thing you might consider (someday), is that it appears to still have the older Ratio Detector transformer installed. That's hardly a dig on your tech at all, as I don't think that until it was determined just what the Wide-Band concept entailed, that nobody even knew to consider the idea of changing the RD transformer out, including myself! In terms of ultimate performance however, it does make a difference.

    Also, you can determine easily enough if the eye tube is responding to the AM stereo sub-channel when tuning in an FM Stereo MPX station with the unit set for MPX operation: Just pull out the middle 12AX7 on the MPX-65 chassis when the station is tuned in. If the eye tube is responding to the sub-channel, it will immediately go wide with that tube removed, and then close again when reinstalled.

    You can also determine if the FM Mono setting is presenting true mono sound (i.e., right off the Ratio Detector), by simply removing the third 12AX7 from the MPX-65 sub-chassis (by the separation control) when the unit is set for FM Mono operation. If it is true mono sound from the detector, removing the tube will not affect the sound in that setting.

    Thanks for the pic!

    Dave
     
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  11. vendo81

    vendo81 AK Subscriber Subscriber

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    Thanks Dave!
    What do I use in place of the RD transformer? I'll do the eye tube and mono tests and will get back.
     
  12. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    ZZ50210-9 RD Transformer from almost any post 1962 FISHER Tuner/ Receiver. This includes Tuner preamps from console's. You can swap them, just remember to reverse the 8uf 50V cap that's installed in the RD circuit, as the Diodes internal to the transformer is reversed from the ZZ592-170.
     
  13. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    Something else to look for. Yay. :p
     
  14. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    A quick look at the Coronet/100-T schematic shows that while they combined the Statesman/202-T's separate Input Selector switch and Stereo/Mono Mode switch into a single 9-position Input Selector switch, it still suffers from the same basic Input Selector switch problem that the Statesman/202-T does: In the case of the Coronet/100-T, there is only one single switch terminal servicing the Channel A input for the settings of FM, FM-AM, FM-MPX, and FM-FM. Since three of these settings require an FM Mono signal be applied to this terminal, while the FM-MPX setting requires the Channel A output from the MPX adapter be applied, it means that in the Coronet/100-T as with the Statesman/202-T, some kind of pre-switching arrangement will be required for the unit to operate as Fisher intended. Without a pre-switching arrangement but with a MPX adapter installed, setting the unit to any mono FM function will simply have the Channel A output from the MPX adapter playing in both channels, which of course is not a true mono signal.

    It does appear that with the use of multiple switch wafer terminals, there is sufficient grounding switch terminals available to provide proper control of an Audio Control relay (and eye tube control relay if desired), so that the unit will respond with FM Stereo MPX functions and indications in the FM-MPX setting, while responding with true FM-mono functions and indications in all other FM settings.

    Dave
     
    Last edited: Jul 26, 2017
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  15. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Who'd a thunk it. 10 years ago here we all were trying to figure out ways to get 400's, 500c's and 800c's running reliably, and now were re-engineering Avery Fisher's stuff in ways that his engineers wanted to but were ham strung by Candy-assed, Penny pinching accountants!!!
     
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  16. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Yep Larry, I think Avery would be proud......Just think of his reaction to LED Lamps, IBAM boards, etc. Avery's German engineers as well. By the way, wheres Chip these days? Al
     
  17. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Far as I know Chip is still in NYC.
     
  18. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    Dave, you characterized the 202T as a tuner mated to a 400C, but it looks like there are at least a few differences in the preamp section. For one, the stereo/mono selector on the 202T only has five positions, instead of the six found in the 400C. I think there might be a different number of input selections, too. I was hoping that there might be some junk 202T chassis out there that could supply switches for my partial 400Cs, but no luck there.

    As it turns out, my scrap 800B chassis has the ZZ50210-9 RD transformer! No need to search for one to hot rod my FM-200!
     
  19. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    The 800B would in fact have the upgraded RD transformer, since it came with a WX chassis installed.

    Dave
     
  20. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    Dave, that's what I thought after my brain clicked over a few times and I remembered that the 800B came with a WX installed. It was a happy moment to verify that the junk chassis has the right RD transformer.
     

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