Fisher 800-T

Discussion in 'Fisher' started by mpr2000, Aug 11, 2018.

  1. mpr2000

    mpr2000 Active Member

    Messages:
    286
    Location:
    Rochester, NY
    I'm working on a Fisher 800-T. This one has the multi-tap power transformer and the owner bought it in Germany new and brought it back here (US) in the 70's.

    I'm going through it for him, and had a question on a cut wire at the power transformer. All the schematics I've seen are for the US market 500/800 units.

    See the pic below - there is a wire that is Green/Light green stripe cut short and hanging. I don't imaging this would have left Fisher like this and the green series wires are usually secondary side and lamp windings/6v.

    Any thoughts? Anyone have an 800-T specific schematic with the multi-voltage transformer? More of a curiosity than anything. I'me wondering if he used it while in Germany at 240v and had it re-wired for 120 when home, but it's not clear. One more indicate it may have been worked on is that some of the wires from the transformer are soldered to the power board, where it appears all others are push connectors.


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  2. fred soop

    fred soop Super Member

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    1,946
    The schematic shows a white/green wire which is at the end of the primary winding and used only for the highest voltages, 240 V or 130 V. The secondary 6.3 V heater wires are green and yellow. Looks like you could stick a meter probe or a short piece of wire to connect a meter probe into the end of that wire, then measure ac voltage to another primary wire.
     
  3. AudioWizard

    AudioWizard AK Subscriber Subscriber

    Messages:
    162
    Location:
    Reno, NV
    Is that a large piece of wire, soldered in where the fuse are supposed to be?
     
  4. mpr2000

    mpr2000 Active Member

    Messages:
    286
    Location:
    Rochester, NY
    Thanks - that helps. I will probe the one wire and see if I see AC there. I'm betting that's the 240v winding.

    The fuses are fuses, and are soldered in place for some reason. Good call though; I will look that over more carefully. There is the one (externally mounted) main AC line fuse that is the correct value correct for 120v.
     
  5. mpr2000

    mpr2000 Active Member

    Messages:
    286
    Location:
    Rochester, NY
    More on the fuses mentioned above. They are in fact "Fuse Jumpers" (only on the 500-TX and 800-T). There is a service bulletin (146) that makes a change. Each emitter of the output transistors has a 4 amp pico fuse in series at each transistor. The bulletin specifies jumpering these fuses, and replacing the two fuse jumpers with 5 amp slo-blo fuses. This is B+ and B- supply.
     
  6. AudioWizard

    AudioWizard AK Subscriber Subscriber

    Messages:
    162
    Location:
    Reno, NV
    So the factory replaced the fuses with soldered-in buss bar (" Fuse Jumpers") and then went back to slo-blow fuses ?
     

     

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  7. mpr2000

    mpr2000 Active Member

    Messages:
    286
    Location:
    Rochester, NY
    It appears that way. See attached bulletin.
     

    Attached Files:

  8. fred soop

    fred soop Super Member

    Messages:
    1,946
    Good design per what we know today is there should be fast fuses of 2 or 2.5 A but they should be in the power leads to the amplifier boards, not on the emitters of the output transistors as originally connected. The slow blow fuses will only protect the power supply after a disaster in the output stage. When the original emitter fuses blow, the drivers are still connected to the load and this can cause additional problems, especially if a shorted load was the original cause. With fuses at the power supply connections to the boards, a blown fuse will shut down the entire amplifier.
     
  9. mpr2000

    mpr2000 Active Member

    Messages:
    286
    Location:
    Rochester, NY
    Good info - I will be doing the SB work to remove the emitter fuses and adding fuses at the PS.
     

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