Fisher MPX Adapters

Discussion in 'Fisher' started by TheRed1, Dec 22, 2011.

  1. larryderouin

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

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    Yes for the Single MPX output and input jacks. Both the MPX-100 and 200 use straight wall voltage. Either plug them in to the AUX POWER Plug or the wall or power strip.
     
  2. FauxHall

    FauxHall Super Member

    Messages:
    1,200
    I'd hate to blow $200+ on a MPX when it needs 2.0V when I can only output 0.1V.
     
  3. larryderouin

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

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    I also have a Sherwood M3x and it works fine on the FISHER's. There was compatibility between manufacturers on this. You're taking the signal for the mpx off the end of the tuner, not the preamp. So the output voltage from the mpx jack will be similar on all of them, plus Most of them have equalizing pots for when you switch from Stereo to mono. No problems with output voltage and input sensitivities.

    Latest project with regards to MPX was converting a 1959 610 consolette to accept MPX. I used the 61 Electra III (Same basic chassis) and rewired the 610 chassis. Connected the MPX-100 and no problems. Also checked it with the M3x and again no problems, plenty of gain.

    Larry
     
  4. FauxHall

    FauxHall Super Member

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    Thanks, Larry D.

    That's just the kind of reassurance I need to proceed.
     
  5. EastPoint

    EastPoint AK Subscriber Subscriber

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    I had a Fisher MPX-75 that was for a console and ran three 12AX7s. It looked like that MPX-78.
     
  6. junkjer

    junkjer New Member

    Messages:
    9
    Fm-100/mpx-65

    Hi-
    Could anyone offer any guidance on connecting an MPX-65 to an FM-100?

    My best guess so far:

    FM-100 connector position #1: Black wire (MPX input) from MPX-65 (the one next to the orange wire on the MPX)
    #2: Orange wire from MPX (FM-100 schematic indicates this connects to a 200v source)
    #3: ?
    #4: ?
    #5: Brown wire from MPX
    #6: Green wire from MPX
    #7: Yellow wire from MPX (the yellow near the black wire on the MPX)
    #8: Shielding from the FM-100 output wires)
    #9: Black wire from MPX (near the yellow on the MPX)

    There is another yellow on the MPX, which appears to be for the stereo multiplex indicator on tuner models that have one -- I don't think the FM-100 does. So I imagine I leave this unconnected.

    This would be much simpler if I knew what I was doing or I had a FM-100 schematic that includes the MPX-65 connections. The schematic I have is apparently for connecting an MPX-20 to the FM-100.

    Thanks for any help you can offer!
     
  7. larryderouin

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

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    The FM 100(NO SUFFIX) has no facilities for a ONBOARD MULTIPLEXER. It does have a jack for an outboard multiplex adapter. The "B" and "C" suffix do have a ONBOARD adapter. You run the high risk of seriously screwing up the tuner or the mpx board by trying to do this without extensive knowledge of the circuits. If you have a FM-100(no suffix, suggest you get a MPX-100 or other outboard mpx unit.

    You Really should make a separate thread on this. Maybe Dave G. would have some idea on this. I will say it's complicated enough to give him a migraine, so most likely the rest of us would have strokes.



    Larry
     
    Last edited: Jan 9, 2015
  8. junkjer

    junkjer New Member

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    9
    Thanks for the advice. I've started a new thread on the subject.
     
  9. Dragunski

    Dragunski New Member

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    6
    Location:
    Alexandria
    I have a Fisher 90X tuner ("Golden Cascode") which I've been using with a Heathkit multiplex - an AC-11. This was a great combination for a couple of years, but then I started having trouble with the Heathkit, a lower signal and and a hum through one channel. I disconnected the Heathkit, and now I use the 90X in mono - it still has one of the richest and most beautiful tones, better than I get from any other tuner.

    But it's mono. Should I look for one of the pricy MPX-100 units from Fisher, or get the Heathkit repaired?

    There's a "restored" MPX-100 on Ebay right now for $350 - which is more than twice as much as I paid for the 90x in the first place. The seller will generously provide free shipping at that price...
     
  10. larryderouin

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

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    The problems with the Heathkit could be as simple as the electrolytic caps needing replacement, a weak tube, or all the way up to a total rebuild/alignment. If you like the way the Heathkit sounded with the FM90X, see how much a shop will charge to fix it. Of course you'll need the schematics for it when it goes in to the shop. And then you need to develop a cost cutoff point for fixing it.

    I use a Sherwood A3mx with my 610 consolette vs my MPX-100. It's better tuned and sounds pretty good with the consolette.
     
  11. Dragunski

    Dragunski New Member

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    Location:
    Alexandria
    Thanks. I'm going to take the Heathkit and get it checked out. I'm pretty sure Bill Thalmann can handle it. But he'll want to re-cap it and it'll cost more than it's worth, maybe as much as a MPX-100! The only problem with the Heathkit is that it's ugly and you have to hide it behind the tuner. When it was working, though, it sounded great.
     
  12. larryderouin

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

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    Dragunski; If you have the skill set, you can recap the multiplex unit's electrolytics. And if you know someone with a tube tester, you can check the tubes for a weak or bad one, then replace any that are not in spec. That in itself should not affect alignment. If it's still giving you problems at that point, take it in for an alignment. As for the MPX-100, it's an unknown quantity at this point, so you'd still have to check it out and possibly do the same thing to it.
     
  13. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    The MPX-100 isn't the world's easiest recap. The chassis is narrow, deep, and absolutely full of stuff.
     
  14. pjt92

    pjt92 Member

    Messages:
    78
    Location:
    Chicago
    I just bought in my Coronet 100t preamp / tuner to have a going through to my audio tech. He surprisingly enough had an out of the box 100t standalone that had the wx mpx in it when he bought it. I also have an 800ta in the shop as well with an mpx 100. After explaining how much a pain in the arse it is to get the 100t to play multiplex with an outboard mpx I asked about using an onboard unit like the 65 or one of the 70 or 75's that seem to be chasis mounting versions. He said he should be able to get the 65 to work almost like the wx board and lucky for me someone I knew had a 500c being parted out so I snagged the 65 for cheep. Now to wait and see how the receiver and pre/tuner come out in the end. Sometimes I wonder if some of the people that hunt down, work on, or collect this gear end up going nuts in the same way the inventor of fm Edwin Howard Armstrong did after trying to get fm into the mainstream.
     
  15. BobHicks

    BobHicks AK Subscriber Subscriber

    Messages:
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    Location:
    Brampton, Ontario, Canada
    I too have a 100T Preamp / Tuner and have been having problems getting a MPX unit to work. I just got my 100T back from repair with bktheking, a memnber here. He tried to install the MPX-65 that I had but was unable to get it to work satifactoraly. If your guy can get it working for you i would appreciate hearing back about how he did it. The 100T was designed to work with the Crosby system and used the MPX-20 which is not being broadcast anymore.
     
  16. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    If I may, installing any version of the MPX-65 -- or its variants -- and having the unit end up operating properly in a manner as would be expected of a Fisher product is quite an undertaking. Some time ago I took on that task with a 202-T, which is the higher tier version of the basic tuner/preamp series that includes the 100T/Coronet offerings in the lower tier. As is so often the case, the particular 202-T I serviced had been through the tech mill trying to get an MPX-65 to work properly in the 202-T chassis. It seems so easy right? Physically, it's a drop in fit, and the connections should be easy enough -- except that they aren't. However, with some thoughtful re-engineering, these units can be made to operate exactly as Fisher would have intended.

    At the heart of the matter is that these units were designed to operate with the MPX-20 stereo decoder, the really never produced design that Fisher came up with to decode the Crosby FM stereo format that Fisher was betting was going to win FCC approval -- except it didn't, and the rest is history. That's why there were so few of these tuner/preamps produced, because they were ultimately an "oops". For those that were, Fisher simply recommended using one of their new outboard units based on the format selected (GE/Zenith), and let the issue quietly go away. But converting them is still so tempting. There are two main issues to deal with: Indication, and mono operation -- both of which are important.

    Because the Crosby format utilized an FM sub-carrier for the stereo information channel, it was perfectly adequate to tune in an FM stereo station by the usual FM signal strength indicator (meter or eye tube), as the strength of the two signals (one within the other) would coincide with each other. The problem is, that the GE/Zenith system uses an AM sub-carrier, whose signal strength doesn't always coincide with the strength of the main FM carrier itself. This is why ALL of the Fisher FM MPX tuners and receivers of the GE/Zenith format base their automatic FM stereo switching or FM MPX Stereo eye tube indications on the strength of the AM sub-carrier of the MPX station being received, NOT the strength of the main FM composite signal itself. But the 100-T, 202-T units don't have any built in ability to handle switching of the eye tube from one type of indication to another. Therefore, even if you get the MPX-65 type decoder to "work", there is still no ability to tune it for optimum separation, let alone indicate that an FM MPX stereo station is being received.

    The second issue is that if the MPX-65 type decoder is installed, you will find that you then no longer have any ability to listen to a distant FM MPX Stereo station -- or any station for that matter -- in true mono mode. Therefore, noisy stereo stations remain noisy, and mono talk radio/news stations must be listened to through the stereo decoder, which is not always a pleasant thing to do.

    These things can all be overcome, but it does take some re-engineering of the unit -- which Fisher simply chose not to do. They just dropped the tuner/preamp line after these models, and went with separate tuners and the 400 CX-2 going forward. A proper install therefore involves installing a small DC switching relay to switch not only to FM Mono audio when selected, but also trigger the eye tube to function as an FM signal strength indicator as originally intended in mono mode, or as an AM sub-channel signal strength indicator when stereo mode is selected. The sensitivity of the eye tube also needs to be adjusted so that it closes part way in mono mode with full composite signal strength, but fully in stereo mode with full AM sub-channel signal strength. In this way, in stereo mode, stereo stations are properly tuned and indicated with full (or near full) closure of the tube, while mono stations only close the eye part way. This is exactly how Fisher chose to deal with these issues in the Fisher 400, allowing the single eye tube to act as an FM signal strength indicator, AM sub-channel signal strength indicator, and FM MPX Stereo Broadcast indicator all at the same time.

    These issues may seem trivial compared to just getting the darn MPX unit to work, but without proper addressing, the beautiful Fishers that these units are just don't come off as working like a "Fisher". Other issues exist as well, but are much smaller and simpler to deal with by comparison. I offer this information to help guide any techs in their efforts to modify these models with an MPX-65 type decoder. Of course once installed, the decoder will also likely need alignment for best separation performance.

    I hope this helps!

    Dave
     
    Last edited: Mar 17, 2016
  17. rwshocker

    rwshocker New Member

    Messages:
    1
    Dave, I also have a 202t and was going to try to install a mpx-120. I can't even find a schematic for the 120, but let's assume that it is similar to the 65. If you still have the 202t I would greatly appreciate a schematic and or pics of the wiring of the 9 pin plug and the relays.Thank you so much.
    Ralph.
     
  18. pjt92

    pjt92 Member

    Messages:
    78
    Location:
    Chicago
    Ok The Only MPX units I have seen installed in a 100t are the wx board which my tech got in a standalone 100t. and now on ebay there is a 100t with a mpx 50 which seems to be an early add on mpx or in some council I'm not 100% certain. My tech just got back to me with my 800ta and mpx100 so he will let me know how much of an undertaking it is. The man has spent 30 years in the audio world and thinks he can engineer a way. There is someone on youtube with an mpx 100 plugged into a 100t. Weather or not it is playing in stereo or not is beyond me but I know from what I was explained is you you can make an mpx 100 work on it but without the indicator tube. You can get the indicator tube to work if you work with it off the blank mpx input in the chassis. I will let you know exactly what my tech says after he finishes so I don't say anything stupid before hand. I will see if he can make some sort of diagram of what he did.
     
  19. vendo81

    vendo81 AK Subscriber Subscriber

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    My 100-T has an MPX-65 in it and everything works perfectly. The eye tube works fine and it switches between mono and stereo when going across the dial as it should using a relay. The 100-T is exceptional on AM and FM. Dave's information in post #36 is very informative in getting one to function correctly.

    Fisher 100-T.jpg Fisher 100-T 2.jpg
     
    Last edited: Mar 17, 2016
  20. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Location:
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    Vendo -- Interesting. So your tech basically installed the FM Automatic circuits for auto switching between Mono FM and FM MPX Stereo? If so, did he install some sort of Stereo Beacon to indicate that the station is broadcasting in stereo? That of course is the other approach to use (as used in the 500C/800C receivers), but installed as Fisher designed it, requires an additional tube. I used the approach that Fisher used for the 400 Receiver, letting the eye tube perform the various indicating functions depending on how the front panels are set. It doesn't require any extra tubes, but does still require a small relay to produce a true FM mono signal when selected.

    RW -- I will dig around and see what I can find on that project. It was for a client so the actual unit is long gone, but I'll check to see what I have.

    Dave
     

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