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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    An interesting hook, since Fisher never produced such an animal.........

    There's not many pieces of Fisher vacuum tube equipment that I haven't seen or worked on. Like everyone else, I have my favorites, but ever since I added a MPX sub-chassis to a Statesman/202-T tuner/preamp for a client some years ago, I was hooked and have always kept my eyes open for one........someday. When Al (Tinkster92) made me aware of one recently available here on AK and decided to pass on it, it was not a hard decision for me to make. A beautiful unit to be sure, but arrived with about a dozen issues needing to be addressed, many minor, a couple typical, and one serious. Once they were all resolved, the unit was set aside, although it saw some brief action recently in the thread on Rob Thomas' TA-800, when that project moved into servicing the MPX-100 adapter which allowed his TA to receive FM Stereo MPX broadcasts. In that thread, the Statesman served to determine just what it was that made a Fisher Wide-Band FM tuner/receiver, "Wide-Band" -- a feature that the Fisher AM-FM Stereo units like the Statesman/202-T did not enjoy. With the TA project finished up and order once again restored in the lab, I had a couple of extra days to play with the Statesman. First up: modify the unit to deliver best possible Stereo MPX performance/operation, using the MPX sub-chassis that Fisher designated for use in the various "B" versions of their tuner offerings (WX), to make the very most of the unit.

    Like the TA-800, the Statesman lived in that small window of time bookended by the reality of stereo records and tapes on one end, and the coming of FM Stereo MPX on the other. In between these two events was the wonderful wacky world of AM-FM Stereo, where there was initially no rhyme or reason to channel identity, or the phase relationship between the two broadcast channels, either. While the channel identity issue ultimately settled out as designating the FM signal for the left channel and the AM signal for the right, the proper phase relationship between the two broadcasts was never established, resulting in the need for a Phase Reverse switch to reverse the phase of one channel if it was received out of phase with the other. For the Statesman/202-T then, Fisher went all out by offering a unit that included two completely independent high quality AM and FM tuners, a 400C preamp, phase inversion capabilities, and space for the future installation of a MPX sub-chassis, to make up the only upper tier stereo tuner/preamp unit that Fisher ever offered. The Statesman tips the scale at 21 tubes before a multiplex adapter is added, with only the TA-600 and 800-C receivers -- with their two built in stereo power amplifiers -- surpassing this count -- by just one tube. The Statesman/202-T does include a muting function that neither of those two receivers have, but does not have the automatic FM stereo switching that the 800-C enjoys.

    As the end of the AM-FM Stereo time window was approaching, Fisher was so convinced that the Crosby system of stereo multiplexing was going to be the approved method that it developed a series of tuners and tuner/preamps based on this system, with a blank plate installed where an appropriate MPX adapter would go at a later date, once the FCC gave the go ahead for FM Stereo MPX broadcasting to formally commence. It's a well known story within Fisher circles, designed to allow Fisher to claim another huge "first" by offering the first truly MPX ready equipment when the MPX broadcasting switch was officially thrown. Mounting with just a couple of screws and connecting via two plugs, adding an adapter to one of these units had to be one of the very first plug-n-play operations in existence, allowing the owner to convert the unit them self. Except of course, that the Crosby system wasn't approved. Oooops.

    With the help of AK members, it was determined that Fisher ultimately did in fact produce a GE/Zenith based multiplex sub-chassis adapter for these units (MPX-50), although they seem to be exceedingly rare. As for the Statesman/202-T, there were apparently a fair number of these units made, as evidenced by service manuals extending to at least serial numbers 30001 to 39999. But even with this many produced, they too are a pretty rare bird themselves. Finding a Statesman/202-T with an MPX-50 installed then is on the order of finding Bigfoot: In all my years of searching, I've only seen one that sold with an MPX-50 installed. All the rest, including mine, were found with the blank plate still firmly in place -- and I think for good reason: Even though the MPX-50 was the specified adapter for the Statesman/202-T, its installation hardly produced that smooth, well engineered FM Stereo MPX operation that Fisher was to become famous for. At issue is the various switching, indicator, and control functions built into the Ooops units that were based on the needs of the Crosby multiplexing system -- needs that are significantly different from those that the GE/Zenith system requires for best performance. As a result, just because a Fisher specified GE/Zenith adapter is dropped into a Statesman/202-T chassis, it doesn't mean that the conversion produces the same great Fisher MPX experience that their later units delivered. In fact, it comes off as quirky to operate, stealing other features from the unit to make it work properly back in the day, and did not deliver all the performance of which the GE/Zenith system is capable of. As a result, all of these units just quietly disappeared, quickly being replaced by "B" version tuners, that were designed for the GE/Zenith based system from the ground up. As for the stereo tuner/preamp concept? Never again did Fisher ever venture into the waters that the Statesman/202-T represented to offer an upgraded B version of that unit, nor for its lower tiered cousin, the Coronet/100-T tuner/preamp either. So what were (are) the problems?

    Next time.

    Dave

    BELOW: The candidate:
    SAM_2110.JPG
    BELOW: Pre-multiplex installation, the Statesman/202T already has one of the busiest landscapes around!
    SAM_2114.JPG
    BELOW: The challenge:
    SAM_2115.JPG
     
  2. RS Steve

    RS Steve Tube Junkie Subscriber

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    Beautiful unit, styling resembles the TA series of receivers. Good thing they didn't have the wording on that MPX cover with the last two words reversed, someone might be offended. :D
     
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  3. larryderouin

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

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    ROLFMAO!!! "Remove this Plate and Plug, DUMMY!

    Now I've got to clean off the Monitor of all this coffee!

    All done. I recapped one for Wharfcreek back in 2013 I think it was. And it was posted about as to how to connect an outboard MPX unit to it. I'll see if I can find it.

    18 minutes later.......... Found the link...... http://audiokarma.org/forums/index.php?threads/202-t-how-to-connect-multiplex.430676/

    And DAVE's original Thread on his 202-T and his quest for MPX..... http://audiokarma.org/forums/index.php?threads/fisher-202t-help.616988/

    Larry
     
    Last edited: Jul 21, 2017
  4. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    First up, as was determined in the TA-800 thread, any of the non-wide-band Fisher units can be converted to wide-band operation by changing out the Ratio Detector transformer used in those models (ZZ592-170), to that used in all Fisher tuner/receivers designed for use with the GE/Zenith multiplex format (ZZ50210-9). If there is no intent to convert or use the older AM-FM Stereo equipment for FM Stereo MPX operation, then there is nothing to be gained by changing out the older detector transformer. In fact, the older transformer will still deliver very listenable FM Stereo MPX performance with GE/Zenith based adapters. But if the very best FM Stereo MPX performance is your goal, then changing out the old transformer is a must. For those familiar with the TA-800 thread, this has already been done in my Statesman unit during the course of that thread. But other significant issues remain. They include:

    1. FM Mono Operation: As designed, this was achieved by selecting "Tuner" on the Input Selector switch, and CH A (FM) on the Mode switch. Selecting the Tuner setting applied the output of the FM tuner to Channel A, and the output of the AM tuner to Channel B. If the Mode switch was then set to Stereo, then AM-FM Stereo operation was achieved. If Channel A was selected on the Mode switch, then Mono FM was produced in both speakers as previously noted, while if Channel B was selected, then AM reception was delivered in both speakers. But a problem develops with this orderly system when the unit has a GE/Zenith MPX sub-chassis installed.

    Of the two Input Selector switch settling that are relevant to FM operation (Tuner and MPX), for Channel B, there are two distinctly different selector switch terminals for these settings, since in the Tuner position, Channel B is handling the output of the AM tuner, and in the MPX setting, it is handling the Channel B output of the MPX decoder. Two different sources, two different switch terminals, so all is good. However, things are no so rosy in Channel A.

    Because Channel A is handling an FM signal in both the Tuner and MPX settings, there is only ONE switch terminal servicing both of these settings, with the rotating switch disk formed so as to make connection with this one terminal in either setting. Understanding this is crucial to the crux of the problem. With the original Crosby based MPX-20 adapter installed, there was no problem: The adapter's Channel A output was always connected to this one terminal. In the Tuner setting, a separate single grounding switch contact is used to switch the MPX-20 into mono mode, so that a mono FM signal appeared at both of the adapter's outputs, while in the MPX position, the MPX-20 was allowed to do its thing, so that only the Channel A signal appeared.

    Now theoretically, the same approach could be used when installing a GE/Zenith adapter. Just use the MPX control switching provided to throw the adapter into a Mono mode of operation, with FM Mono then appearing at each of the adapter's outputs -- except that for the type of MPX control switching provided, there is no easy way to throw a Fisher GE/Zenith based adapter into FM Mono mode -- not using good engineering practice anyway. The only control system available is a single switch contact that is grounded in the Tuner setting, and open in the MPX setting. With that approach, you could achieve Mono operation by:

    1. Grounding the input of the 38 kHz oscillator trigger stage -- but that would remove all bias from that section of the tube shortening the life of that section significantly. It also leaves 38 kHz artifacts in the mono outputs because the oscillator is still operating.

    2. Grounding the grid of the 38 kHz oscillator stage -- but that produces the same result as #1 above with regards to tube life, shortening it in the oscillator section.

    3. Grounding the grid of the Pilot Amplifier stage -- but again, 38 kHz artifacts would still remain.

    And that's about it, with no really good solution available from the control switching provided. Because the Crosby multiplexing system does not require the use of any on-board oscillators, and uses two separate signal sources to generate its stereo output, it becomes a simple matter of grounding out the multiplex sub-channel signal to obtain mono operation of the adapter. With a GE/ Zenith based adapter, about the only way to throw it into mono mode would be to short the stereo outputs together. But that approach will not work in the Statesman/202-T, because the single grounding switch terminal (that works in connection with other terminals requiring grounding when called for) doesn't have two isolated contacts that it could be used to short the outputs together. And even if output cross-coupling switch terminals were available, even that approach gets shot down, because when set to the Tuner position, the Channel B output of the adapter is grounded to prevent crosstalk with the AM signal selected there in that setting. If the Channel B output is grounded in the Tuner setting, and its cross-coupled to the Channel A output in the Tuner setting to effect Mono operation, then the Channel A adapter output is effectively grounded as well, meaning that there would be no Mono FM signal to be had in the Tuner position. There is simply no way to properly switch a Fisher GE/Zenith adapter into Mono mode in the Statesman/202-T chassis.

    It is important to note that being able to achieve FM Mono operation is important with the GE/Zenith system, since:

    1. Back in the day, many stations were still mono in the early days of FM Stereo MPX broadcasting. There are also many news/talk FM stations today that do not broadcast a stereo signal -- this to maximize their range. With the GE/Zenith system, audio quality is compromised when listening to mono broadcasts through the adapter (due to the presence of 38 kHz artifacts in the audio output from the output of the 38 kHz oscillator that continues to operate), so some means of achieving FM Mono operation is important to maintain high quality audio output when FM Mono stations are received. Also note that Fisher clearly addressed this issue in their GE/Zenith tuner/receiver designs by choosing either the output of the MPX adapter in stereo mode, or the output of a separate mono audio path from the Ratio Detector (with its own de-emphasis network) in FM Mono mode. When stereo mode is selected, the output of the separate mono audio path is grounded -- which is important in placing the proper load on the output of the ZZ50210-9 transformer to achieve maximum separation.

    2. When desired FM Stereo MPX stations are just too noisy to receive, the only real recourse is to listen to the station in FM Mono mode, this to eliminate the noise from the AM sub-carrier contained in the Stereo MPX composite signal.

    So even though FM Stereo MPX is still the main name of the game today, being able to select FM Mono operation at will is still important to achieving proper tuner operation. To give an indication as to just how important but convoluted this whole issue was to Fisher if (heavens forbid) the Crosby format didn't win out, they knew that with the GE/Zenith system, the ability to still be able to receive FM broadcasts in mono (when needed) was important enough -- and particularly if you ended up using the Statesman/202-T with a different (i.e. less compatible) manufacturer's MPX adapter -- that they provided a little understood if-all-else-fails AUX / FM AUX switch on the back of the unit. This switch absolutely provided for the reception of any FM station in FM Mono mode -- by way of the Aux Input switch setting if the rear switch is so activated, in case all else fails.

    The whole process of moving from FM to AM-FM Stereo (and its variants) to FM Stereo MPX was messy, convoluted, and barely understandable half the time even when it was actually happening let alone 55 years later, due to all the different nuances involved. But understanding the importance of the finer points is important if the effort is made to bring the older Fisher gear up to all it was intended to be with regards to receiving FM Stereo MPX broadcasts.

    Next up, problem #2: The tuning indicator, and indicating when an FM Stereo MPX broadcast is being received.

    Dave
     
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  5. gadget73

    gadget73 junk junkie Subscriber

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    How did they handle phase inversion in this, switching output between plate and cathode of a tube? My Sherwood S-7000 does it that way. The feed for the left channel power amp can be selected off the cathode or anode of the last tube in the tone control section. Makes a hell of a pop when you throw the switch too since it has to discharge the unloaded coupling cap. Oddly my Pilot simulcast tuner/preamp has no provision for phase reversal, nor does the power amp. Possible it would have been handled with an external speaker switch arrangement in it's native console environment.
     
  6. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Great to see this thread, been waiting for it, very glad you have this tuner/pre Dave. Will be a learning experience for us all. I've seen this in person and pics don't do it justice at all. A real beauty! Al
     
  7. Westy56

    Westy56 A symphony of paradox

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    Dave, can the hh scott 335 multiplexer work in place of the onboard one that goes with the 202t?
    This is my favorite sounding tuner in my setup. It's already converted me to mono FM listening.
     
  8. walyfd

    walyfd Well-Known Member

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    What year Statesman is this from and is it any different from the standard version?

    The early '60's was the epitome of the tube era... from 1959 to about 1962/63, things were evolving at such a pace. And the build quality was impeccable.
     
  9. audmod01

    audmod01 AK Subscriber Subscriber

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    Dave;

    How broad is the tuning of the ZZ592-170 Ratio Detector compared to the ZZ50210-9 Ratio Detector? I know that getting below about a 150kHz bandwidth for many tuners does begin to restrict ability to handle the MPX signal. I remember H H Scott and Fisher both lauding the benefits of wide-band detectors years ago, but at the time if I read much about it I have long since forgotten. On modern tuners with multiplex circuitry the 150kHz bandwidth ceramic IF filters are considered the lowest bandwidth filters that area acceptable. Most generally go with 180kHz or wider and use several in sequence to obtain the IF response they want. Distortion is a consideration too and the group delay of the filters gets into the act there.

    Joe
     
  10. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    So the bottom line of problem #1 is, if you simply install a GE/Zenith based sub-chassis without doing any other modifications, and turn the Input Selector Switch to Tuner and Mode Switch to Channel A, you will in fact hear the same identical sound out of both speakers: Both speakers will be reproducing stereo Channel A from the MPX decoder, which is NOT the same as L+R Mono FM. And using the the Aux input option via the back panel switch to achieve Mono FM sound is hardly a good option, either.

    The easiest way to resolve the Channel A signal issue is to install an Audio Control Relay. It can take the single common input terminal for channel A for both the Tuner and MPX positions, and toggle it between a true mono signal derived directly from the Ratio Detector (as Fisher did) when the Input Selector is turned to Tuner, or the Channel A output of the MPX sub-chassis when the Input Selector is turned to the MPX position. And, it can easily be controlled by the single terminal grounding switch on the Input Selector switch that is closed or open in Tuner or MPX positions respectively. As well, if a miniature sealed type 12 volt DC relay is used, then it can be powered from the DC heater supply, eliminating any problems with hum and contact contamination. And finally, if a DPDT type relay is used, then the un-selected relay signal can be shorted to ground as well to prevent any cross-talk between the relay signals. Such relays are inexpensive, and their use complete resolves the Input Selector/Mono FM/FM Stereo MPX switching problem:

    1. With the Input Selector switch set to Tuner, then:
    A. With the Mode switch set to Stereo, the unit plays Mono FM out of the Channel A speaker, and AM out of Channel B speaker as it originally did.
    B. With the Mode switch set to Ch A (FM), the unit plays Mono FM out of both speakers as it originally did.
    C. With the Mode switch set to Ch B (AM), the unit plays AM out of both speakers as it originally did.

    2. With the Input Selector switch set to MPX, then:
    A. With the Mode switch set to Stereo, the unit plays FM Stereo MPX as originally intended.
    B. With the Mode switch set to Ch A (FM), the unit plays FM Stereo MPX Channel A out of both speakers.
    C. With the Mode switch set to Ch B (AM), the unit plays FM Stereo MPX Channel B out of both speakers.

    Problem solved.

    It is interesting to note the original intended operation of the unit for settings 2B and 2C above, versus how the unit now operates on these settings. As modified, these settings are simply directing either Channel A FM Stereo MPX signals to both speakers, or Channel B FM Stereo MPX signals to both speakers. The settings aren't particularly useful unless you enjoy listening to 60's exaggerated stereo, and only want to hear the Mamas from stereo Channel A out of both speakers, or the Papas from stereo Channel B out of both speakers. But at least, the operation of the unit as modified on these settings makes perfect sense versus how the switch settings are labeled.

    Originally however, that was not the intended use of the 2B or 2C settings at all. As originally designed, when the unit was set as described for 2B, the unit played L+R Mono FM out of both speakers, just as it would when set as described for 1B as well. However, in the 2C setting, the unit would then play a L-R signal out of both speakers, which is the stereo sub-channel generated from the MPX-20 multiplex decoder when/if it was ever installed. I suppose the idea was to toggle the Mode switch back and forth between the 2B and 2C setting, while adjusting the "MPX Stereo Control" on the back of the unit for equal sound level between the two settings with certain broadcast material. In this way, you adjusted the MPX-20 sub-chassis for maximum stereo separation performance. I suppose that had the Crosby concept ever come to fruition, there may have been test tones broadcast to aid in setting the control rather than trying to set it with standard broadcast program material, but that was almost surely the idea behind that strange little MPX control on the back of the Statesman/202-T unit. Of course, its wiring, as well as some other needless wiring designed to make the Crosby MPX Stereo function properly has been removed since it serves no use in a GE/Zenith format setting. With the blank plate and dummy plug installed, the 2B and 2C settings produce no sound at all.


    OK. So (finally) moving on the problem #2.


    As designed, the FM eye tube of the Statesman/202-T was (when activated) a full time traditional FM signal strength indicator. That's it, that's all it did, whether the Input Selector switch was in Tuner, MPX, or Aux with the rear panel FM Aux switch activated. It indicated the relative strength of the main carrier frequency being received, so that tuning for maximum closure resulted in the maximum signal strength being received.

    With the Crosby MPX Stereo format, no other type of tuning indicator is needed, since both the main carrier and the stereo sub-carrier within it are FM signals. Therefore, when the signal strength of the main carrier is maximized, so is the stereo sub-carrier within it. It is inconvenient however that apparently, the Crosby multiplex system had no easy provision provided as to know when a stereo station was being received, other than the (hopefully) obvious stereo sound produced. But that was it. An oversight maybe, or maybe just an unfortunate byproduct of the system. But either way, the Statesman/202-T did not have any provisions to indicate reception of a stereo station no matter what multiplexing format was approved, or what MPX sub-chassis might end up being installed in it.

    With the GE/Zenith system however, while it provides for an easy means of detecting an FM Stereo MPX broadcast, for the best stereo performance, being able to tune the main carrier to achieve the maximum signal from the AM double side-band suppressed carrier stereo information sub-channel provides for maximum stereo performance, versus simply peaking the main carrier for maximum signal strength. The two peaks should ideally occur at the same point, but often that does not happen in practice due to a variety of reasons. As a result, on Fisher Wide-Band Multiplex models with an eye tube, that tube is always indicating the signal strength of the AM DSB sub-channel when in FM Stereo MPX mode to maximize stereo performance. In FM Mono mode, if no other signal strength indicator is provided to indicate the strength of the main carrier (i.e., a meter), then the eye tube reverts to acting as a standard main carrier signal strength indicator in that mode. In models with FM Automatic stereo switching, the auto switching is triggered via the signal strength of the DSB sub-channel, while the tuning meter indicates the signal strength of the main carrier frequency. In all cases then, when set for FM Stereo MPX operation, the tuning process is maximizing the signal strength of the DSB sub-channel. But of course, in the Statesman/202-T, no provisions were made for the eye tube to react to the GE/Zenith's sub-channel signal strength, and as previously noted, there are no provisions for indicating reception of of a FM Stereo MPX signal, either.

    Within the Fisher Wide-Band stable, there are three models that show how they treated eye tube performance when it is being used to indicate both FM main carrier signal strength, and the AM DSB sub-channel signal strength (i.e., the eye tube is the only signal strength indicator): The 400, 500B, and 800B receivers. No other models require such double duty of the eye tube's operation. It's operation in these models can be summarized as follows:

    1. In FM Mono mode, the eye tube acts as a standard main carrier signal strength indicator, with the tube reaching a maximum closure of about mid-way, when tuned to any strong station, mono or otherwise.

    2. In FM Stereo MPX mode, the eye tube will show little closure when tuned to a mono station -- this to indicate that a mono station is being received, and that the unit should therefore be switched to FM mono mode for reception of this station, and best audio quality. When switched, it will then act as described in #1 above.

    3. In FM Stereo MPX mode, the eye tube will show nearly full closure when tuned to an FM Stereo MPX station, this to indicate that a FM MPX station is being received, with the tube responding to the signal strength of the AM DSB sub-channel. Full closure of the beams in this mode was never a goal (although sometimes happens), so as to maintain the effectiveness of the beams as a signal strength indicator.

    In this way then, the eye tube on all three of these models serves the dual purpose of not only allowing for tuning for maximum signal strength of the appropriate signal for the type of signal being received, but also clearly indicates the type of signal being received. It was really quite an ingenious setup that many folks don't realize about these Wide-Band receivers.

    Of course as previously stated, there are no provisions in the Statesman/202-T for the FM eye tube to act in such a fashion, so once again, modification is required to make the MPX retrofitted unit really act and perform like its Wide-Band brethren of the future would come to be known for. And once again, a miniature 12 volt DC DPDT relay comes to the rescue, this time acting as an Eye Tube Control Relay, with itself being controlled by the same single terminal grounding switch used to control the Audio Control Relay discussed earlier. In fact, to simplify things, the two relay coils can be connected in series for 24 vdc operation, still controlled by the single terminal grounding switch on the Input Selector switch, but now powered directly from the 24 volt DC heater power supply. With the installation of an Eye Tube Control Relay, all three of the FM eye tube reactions as discussed above can be created in the modified Statesman/202-T, making its FM Stereo MPX performance not only on par with the best Wide-Band units that Fisher offered, but second to none.

    Next up, I'll show the results that all this planning produced when implemented -- next time.

    Dave
     
  11. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Westy -- It should certainly be able to. But for best MPX performance, the characteristics of the tuner and MPX unit should be wed, so it would take testing to ultimately know how effective the performance from that combination of units would be. I think I have a 335 hidden back somewhere in storage. When I get a chance, I'll try and dig it out to see just how well it might perform.

    Walyfd -- Mine is serial number 20388A, and I know that service manuals exists up to at least 30001 to 39999. Beyond that, I don't know. Larry would be the go to on that one. I do know that there a number of changes made to the units along the way, with most of them occurring at the break starting with 30001 units and higher. Again, as for which year mine if from -- Larry?

    Joe -- I haven't had time to actually measure the response difference between the two transformers, but I am generally of the understanding that wide-band response during the height of the vacuum tube MPX years typically meant a response of about 260 kHz. I believe the response of the older transformer was to about 150 kHz, but I will try to research this for more detailed information. In actual use, I do not perceive any tuning differences between the original and the later transformers.

    Larry -- Earlier versions of the 202-T in fact used a phase splitter exactly as you describe, and is the circuit included in my unit. Later >30000 units used the more complex circuit that Fisher designed, using a single triode as an anode follower phase inverter.

    Thanks all for following along!

    Dave
     
    Last edited: Jul 22, 2017
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  12. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    With the issues of converting a Fisher MPX-ready tuner/preamp intended for Crosby MPX operation into a functioning tuner/preamp using the GE/Zenith MPX format all laid out -- and to the level of detail execution that Fisher's Wide-Band MPX products ultimately rose to when using its tuner based WX sub-chassis decoder, it can be seen why that -- along with other factors -- Fisher ultimately scrapped the idea of moving forward with any "B" version of their tuner/preamp products. The idea of "separates" was already on the outs at Fisher, while complete receivers and integrated amplifiers were the hot new ticket at the time. In fact, of Fisher's "separates" components, it was really only their line of tuners that continued on with the release of succeeding newer models, as after the 400CX-2 and the SA-1000, those product lines of separates ceased any further releases.

    For those who have either of Fisher's stereo tuner/preamps however, when properly converted, they can be one slick ticket -- on top of an already neat unit. All of the Fisher form and function, but with any power amplifier you wish to use. At the very least, it cuts the weight of any of their stereo receivers in half -- important as you get older. The Crosby based stereo tuner/preamps are rare enough and nice enough, that any MPX conversion is deserving of the best retrofit possible, as if Fisher had designed the unit for GE/Zenith based operation from the get go. The following pics show how the basic project unfolded, and the ultimate outcome. It is not meant to be a specific step-by-step presentation, as the process is not particularly simple. Rather, it's an effort to show the details that need to be attended to for a thorough and proper conversion of the unit, and the results that can be achieved:

    BELOW: As seen in the TA-800 thread, the unit is first converted to Wide-Band operation, by changing out the existing Ratio Detector transformer from this one:
    SAM_2111.JPG
    BELOW: To this one -- also as seen in the TA-800 thread.
    SAM_2112.JPG
    BELOW: Along the way, a WX sub-chassis needs to be acquired:
    SAM_2116.JPG
    BELOW: Recapped, and modified with an RCA input plug. This pic is nearing the end of this process:
    SAM_2118.JPG
    BELOW: Recapped, input plug added, ready to go:
    SAM_2119.JPG
    BELOW: Installed in the unit:
    SAM_2138.JPG
    BELOW: Underneath, things get busy in a hurry. Even without the MPX sub-chassis installed, the area originally filled out with wiring under the chassis is dense. With the adapter installed, it becomes a candidate for Fisher's most densely packed chassis. At a tube count of 24, it would be hard finding any other Fisher model so densely packed with vacuum tube electronics, even requiring the use of vertical T-Strips in many places. To the right of the sub-chassis, you can see the Audio and Eye Tube Control Relays. Between them and the sub-chassis, standing up on end is the added B+ decoupling cap to help create the new 135 volt B+ source that the WX chassis requires for its audio circuits. It is sourced from the 160 volt WX sub-chassis power, which itself is derived from the main tuner B+ distributed throughout the tuner circuits. The two vertical T-Strips just above and below the RCA MPX jack were originally used for components associated with the dual mono de-emphasis networks that the Statesman/202-T originally employed as part of the Crosby ready design. The bottom one now supports the dropping resistor for the new 135 volt sub-chassis B+ supply rail, while the upper one now supports components for the new mono de-emphasis network and MPX indicator output. Note too the new RF choke installed (included in all Fisher Wide-Band designs) along with the new Ratio Detector transformer that is installed just to the right of the control relays. There has been other worthwhile work done to this unit to update it to the version that succeeded mine (> 30000), and there is work still yet to be done. The description concentrates on the work associated with the MPX conversion of the overall project.
    SAM_2123.JPG
    BELOW: All buttoned up and operating again:
    SAM_2136.JPG

    Next up, how operation of the Statesman/202-T has changed.

    Dave
     
  13. larryderouin

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

    Messages:
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    Location:
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    The 1960 Statesman 1010 console used chassis from 10001-19999. The 1961 S-70 Statesman manual does NOT list what serial's are covered. To my knowledge the 202-T was either a console specific unit (1960-61 Statesman) OR had a limited run as a separates unit also. If the Front plate says 202-T on the front it's a stand alone unit (aka the TA-800) but if it says Statesman in script along the upper corner (usually the LEFT Side as you face it) it's been torn from a console. I would surmise the changes between Stand-Alones and Consoles would be small and isolated mainly in the Tone control caps to limit the amount of bass in the console version. If Fisher did the same thing with the 202-T as it did with the 800c's in the 1963 executives and standalone 1963 stand-alone 800c's, the 10001-19999 would be 1960 Consoles, 20001-29999 would be 1960 stand-alone, and 30001-39999 would be for both versions in 1962.

    This is supposition on my part, but it is plausible as FISHER did it 2 years later in the 800c.
     
  14. walyfd

    walyfd Well-Known Member

    Messages:
    637
    Location:
    Northeastern PA
    So, following that logic, there would or could have been 1000 consoles of each name by the serial number range.
     
  15. larryderouin

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

    Messages:
    19,961
    Location:
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    Theoretically yes, but the higher end consoles never had the sales volume that the mid range did. For every Executive you find, there's a boatload of Custom Electra's, Futuras, Ambassadors, out there. And the ratio goes higher for the Statesman/Regent and higher for the President.

    Until someone comes up with an intact S-70 Statesman, we''ll never know for sure if the supposition is right or not.
     
  16. Westy56

    Westy56 A symphony of paradox

    Messages:
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    Location:
    Abq, NM
    This has been a great thread on a piece I hold dearly. I love the sound signature of the 202t.
    Looks like one of mine is the last rendition (31137).

    I can't think of a Fisher setup I've heard that sounds as good as the Statesman and Citation II.

    Thanks you guys for all the extremely detailed information. :)
     
  17. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,846
    Location:
    Ball Ground, GA
    The next series of pics shows how the FM eye tube now reacts to different stations under different front panel control settings in the modified Statesman/202-T:

    BELOW: For reference, the unit is set for Stereo MPX operation, and the tuner dial is set in between stations, so that the eye tube beams are fully retracted. Stereo MPX operation is achieved by setting the Input Selector switch to "MPX", and the Stereo/Mono Mode switch to "Stereo":
    SAM_2164.JPG
    BELOW: The unit is still set for Stereo MPX operation, but now the tuner is tuned to 95.5 mHz (WSB) out of Atlanta, which is a MONO news/talk format station. Notice that the eye tube beams have extended inward slightly, but largely remain open, which indicates that: (1) The unit is set for Stereo MPX operation, but: (2) It is tuned to a Mono station, so that: (3) It alerts the operator to reset the front panel controls for FM Mono operation.
    SAM_2163.JPG
    BELOW: The unit is still set for Stereo MPX operation, but now the tuner is moved up the dial slightly to 97.1 mHz (WSRV) also out of Atlanta, and a sister station to WSB above. It is a Stereo MPX rock venue station. Notice that now the eye tube beams extend inward significantly, nearly touching, to create the classic Fisher indication of reception of an FM Stereo MPX broadcast. The eye tube beams are reacting to the relative strength of the AM DSB stereo sub-channel within the main carrier, so that tuning them for minimum gap produces maximum stereo performance.
    SAM_2162.JPG
    BELOW: Now, the unit is set for FM Mono operation (Input Selector switch to "Tuner", and Mode switch to "CH A (FM)"), and the tuner has be re-tuned to 95.5 mHz (WSB) again. Since that was previously determined to be a mono station, this is the appropriate setting for listening to that station. Notice that the eye tube beams extend inward, but not as far as they do when indicating reception of a stereo station when set for that mode. In fact this is exactly how the beams reacted with the stock unit, before installation of the MPX adapter, when it received all stations in mono. To that point, in the FM Mono setting, it still receives all stations regardless of broadcast type in Mono in this setting, with the eye tube beams reacting to the relative signal strength of the FM carrier on all stations.
    SAM_2165.JPG
    BELOW: As for FM Stereo MPX performance, nothing gives a better snapshot of MPX performance than when a dual trace scope is set for identical sensitivity on both channels, and the stereo outputs of the Statesman/202-T are balanced for identical output (via the front panel balance control) using the FM Mono setting (which bypasses the MPX sub-chassis), and then fed to the scope. The unit is then set for Stereo MPX reception, and a L-only or R-only signal is broadcast to the unit. This is a very tough test to pass, because it means that the signal is passing through all of the tuner circuits and MPX adapter for display on the scope. The screen shot below is of the modified Statesman/202-T receiving a L-only signal, broadcast from a Fisher Model 300 Multiplex Generator. The sine wave is the left channel signal, while the flat line running through it represents the right channel. This is a textbook waveform, measuring 39 db of separation between the L and R channels. A R-only signal produces a virtually identical waveform, producing 38 db of separation between the R and L channels. For vacuum tube "time division" MPX decoding -- which at the time is the best there was -- it doesn't get any better than this:
    SAM_2122.JPG
    BELOW: Enjoying a little Eagles and Fleetwood Mac as I work to close this out.
    SAM_2166.JPG

    About the only other comment I could make regarding this unit -- which is honestly quite minor -- is that it is somewhat more critical of tuning than a true Fisher produced Wide-Band product is. This has nothing to do with anything electronic regarding the unit at all, which is in fact quite UN-touchy in that regard. What I am referring to relates to the mechanical aspect of the unit, where having a given rotation of the tuning knob produce less rotation of the tuning capacitor would be nice. But again, this is hardly an issue in use but rather, more in the category of an observation.

    Edit -- The more I use the finished unit (relative to the FM work), the more I think I was premature in my comment above about the tuning. In checking it against my R-200 tuner, I find the two units to react identically tuning wise, with my initial observation of the Statesman/202-T's tuning more the result of antenna orientation relative to the thick summer foliage we have in the northern Atlanta suburbs now due to all the rain we've had this year.

    Dave
     
    Last edited: Jul 22, 2017
  18. RS Steve

    RS Steve Tube Junkie Subscriber

    Messages:
    7,414
    Location:
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    Amazing work as usual Dave, love seeing the rare units get brought back better than new. :thumbsup:
     
  19. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    32,777
    Location:
    Southern NJ
    Would it be possible to fit larger wheels on the tuning condensor? Not sure how close those get to the bottom of the chassis, but that would buy you some. The end up at the shaft looks relatively small already, probably not much to be gained there.
     
  20. vendo81

    vendo81 AK Subscriber Subscriber

    Messages:
    1,495
    Location:
    California
    Very nice work Dave! Very nice looking 202-T. I think I had sent you photos of (the guts) of the MPX-50 that came in my 202-T. My preamp/tuner is still unrestored and hoping it works OK with the MPX-50 installed.
    202-T is serial number 31521D. Here's the MPX unit.



    MPX50.jpg
     
    Last edited: Jul 23, 2017

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