The End of an Era: The Fisher 55-A

Discussion in 'Fisher' started by dcgillespie, Mar 3, 2015.

  1. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    The part has little if any dissipation to it. I used a .5 watt unit in the amp I had here, but a 1/4 watt would work just fine as well.

    Dave
     

     

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  2. blabla_19_d

    blabla_19_d New Member

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    Hi guys,

    Hoping to get some info on 50a or 55a on which consoles they came from. Anybody has information?

    Regards,
     
  3. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    My pair of dream amps one day....:rolleyes:
     
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  4. blabla_19_d

    blabla_19_d New Member

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    Mine as well.
     
  5. blabla_19_d

    blabla_19_d New Member

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    Hi guys,

    Anyone have a full schematic with parts list for the 55a? Is it even possible to clone this amp?

    Regards,
     
  6. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Last edited: Apr 30, 2018

     

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  7. blabla_19_d

    blabla_19_d New Member

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    Thank you. Im really hoping to get one these amps someday. Or maybe clone them if its even possible
     
  8. carlosmattos

    carlosmattos 'Penso logo existo!'

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    Hi Dave,
    Perhaps you can help...
    I have searched for more then 10 years for another Fisher 55A amp to make a stereo pair and not only i found another 6550 type to match the existing,but found also a El34/GZ34 unit.
    To start to try to understand the scheme I started to restore the EL34 unit:all capacitors replaced, and all resistors that were out of tolerance.I had trouble in finding a good replace gor the 80uf 500v filter cap,i replaced with two 200uf 450v in serie as i’m using a pair of 5AW4 rectifying tubes,that will give 100uf at 900v,enough to deal with the inicial voltage surge...but,always a but:
    Have 420v on the EL34 plates and -42v as it should, but the power monitor pointer don’t move at all...
    I suppose that after starting should go to 0?...the only way to put mine at 0 it’s to drop the negative voltage to -24v...
    It’s my power monitor out???

    Best regards
    Miguel
     
  9. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Answered via PM.

    Dave
     
  10. hunter00

    hunter00 Super Member

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    one of my Fisher 50As came in a manufactured cabinet along with a garrard rc 80 TT and 70r tuner /preamp DSCF1112.JPG
     
  11. Jay Towne

    Jay Towne New Member

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    Thanks a lot for sharing your knowledge about these heavy beasts! I've just acquired a Fisher 55A amplifier and a Fisher 80-T AM/FM receiver and pre-amplifier. The seller repaired both. I listened to them at the previous owner's place and although he used a pair of low power speaker boxes, this combo produced was amazing. I haven't installed them yet, it will take some drilling and a lot of muscle (I'll do some warm up before lifting the amp). These two Fisher units have travelled a lot, for I live in southern Brasil.
     

     

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  12. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Welcome to Audio Karma Jay! I'm glad you found the thread useful. You might also like another thread of mine here:

    http://www.audiokarma.org/forums/in...ginal-bad-boy-the-50a-power-amplifier.804905/

    The 55A is basically a warmed over 50A. I mean no disrespect by that comment, but do mean to imply that the two are very closely related, sharing most of the same parts, with the 55A being an upgrade over the 50A primarily with different rectifier and output tubes, on board metering to set the bias with, and a revised negative feedback network. The basic amplifier and power supply circuits however are largely the same. Is yours the version with 6550 output tubes or EL34s?

    Congrats of finding one -- and getting it to Brasil!

    Dave
     
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  13. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    A BIG box greeted me this afternoon when I got home. I asked my 7 year old to move it. He couldn't.
    D32B0AB9-6333-446D-BA58-CC604FC8E131.jpeg
    DCC3126C-F623-4D4B-8AA3-80CC6ED6B3A7.jpeg
    2049C7F6-FB70-445F-9536-74DE23240D41.jpeg
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  14. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    You've got quite a project ahead! Was somebody using input transformers to drive this with at some point? What are the two white octal sockets for -- transformers or preamp power supply plugs? They don't appear to be original.......

    Nice find -- good luck with it!

    Dave
     
  15. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    Dave,

    No idea about the two white sockets. I plan on reverting to stock. I have a few projects on the front burner, but want to get to this sooner than later.
     
  16. hunter00

    hunter00 Super Member

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    Congrates on aquireing the 50A.A few of us here have pairs and became big fans of these old Fisher amps upon first hearing them.Good luck with the restoration project,do you plan on sourceing a second for a stereo pair?Ive tried numerous vintage preamps with mine and settled on a Fisher 400c.
     

     

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  17. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    Looks like they both tie into pins 1 and 5 of the 12AU7 that is near them. Not sure what the purpose of the cap and resistor are.
    I'll draw a little diagram later and post.
    522C70CF-7CA2-4538-BF8D-4CE0FE61A9F2.jpeg
     
    Last edited: Mar 15, 2019
  18. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    Oh and yes, I'd be all in for another 55A if one turns up, though reading through this thread it seems like there are a few people with a single and a desire to add one. I have a 400C I can use with a pair of these, though I use a 202T in daily rotation for the tuner capability. I have a single 80AZ I can pair this with just to let them see some action until units to complete pairs show up - also has the benefit of the balance control not being set in the middle.
     
  19. gadget73

    gadget73 junk junkie Subscriber

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    1 and 5 makes no sense. 1 is a plate, 5 is a heater connection. Not sure what someone would need there.

    Mods where holes are knocked into the chassis kind of bother me, especially big holes that are difficult to plug up later. So says the guy looking at a big ugly amp on my bench and plotting where to drill holes in it.
     
  20. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    I'll look more closely tonight. Chassis plugs the right color and a cage will hide the holes. I felt like the price was right enough that I ought to go for it - especially considering I haven't seen this model on the market that I can recall.

    Anyone had a cage made? I think I ought to start my own thread here...
     

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