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Saw this Fisher stereo EL-84 tube amp online-any idea the model?

Discussion in 'Fisher' started by Greg Nal, Nov 5, 2018.

  1. Greg Nal

    Greg Nal AK Subscriber Subscriber

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    upload_2018-11-4_23-16-15.png

    Listed on an online forum, seller didn't know the model, and no model listed on the chassis. Was a console pull.
     
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  2. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    SA-16! Most likely from a 1960 or 61 Coronet (C-808 or C-55 models).
     
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  3. Greg Nal

    Greg Nal AK Subscriber Subscriber

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    Thanks Larry you're a great resource!
     
  4. Tim D

    Tim D AK Subscriber Subscriber

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    Geeze. How does he do that? :dunno:
     
  5. gadget73

    gadget73 junk junkie Subscriber

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    He's the Fisher Whisperer.
     
  6. Tim D

    Tim D AK Subscriber Subscriber

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    He should put that in his tag line. lol

    For the OP, that's a pretty chassis.
     

     

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  7. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    When you have 11 consoles, 9 of which are various FISHER's you tend to remember most if not all console chassis's by sight.

    Edit; Signature changed......
     
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  8. Tim D

    Tim D AK Subscriber Subscriber

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    Lol. You're funny Larry. :rflmao:
     
  9. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    You been talking to my Girlfriend???? :naughty::music:
     
  10. lilwing

    lilwing CAGE FREE AUDIO ZOO Subscriber

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    20181108_083730.jpg 20181108_083757.jpg Here's what my SA-16 looks like.(sorry for the dust) Similar but has a pair of rectifier tubes. It's a beautiful little gem but not quite as handsome as the OP's amp. IMO.
     
    Last edited: Nov 8, 2018
  11. Tim D

    Tim D AK Subscriber Subscriber

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    Hey FISHER Console Whisperer,

    Why does that one look different than the OP's pic? The whole chassis layout is different. Different year maybe?
     

     

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  12. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Yep. I've seen both variants in different consoles. Can't remember which was in which , but both were Coronets.
     
  13. bhamham

    bhamham AK Subscriber Subscriber

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    Fisher console whisperer! I like it - well deserved.
     
  14. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    I think the OP's is the forerunner of the true SA-16 like lilwing posted a pic of. Both have dual rectifiers, but note that the OP's has only 8Ω and 16Ω outputs and a single pair of inputs, where as the SA-16 has a full set of 4Ω, 8Ω and 16Ω output taps, and a dual set of input jacks. The SA-16 also uses a 12AX7 phase inverter driver tube with AC Bal adjustment pots allowing for greater performance and sensitivity, whereas the OP's uses 12AU7s in that position, and (apparently) no AC Bal controls. After the SA-300, Fisher basically eliminated the 12AU7 from its design arsenal, which almost surely dates the OP's unit to before production labeled SA-16 amplifiers. Interesting that the OP's doesn't seem to show a model number.

    Edit -- Also note that the OP's unit is only labeled for EL84 output tubes, whereas the SA-16 is silk screened for the much more commonly seen designation of 7189-EL84-6BQ5.

    Dave
     
    Last edited: Nov 8, 2018
  15. TheRed1

    TheRed1 Console Conservationist

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    Dave is on the right track. I'm not sure of the relation of this model to the SA-16 - perhaps Dave could compare schematics and give us a brief analysis. I believe this is Fisher's original "1000" amp from the 1958 Executive II. Schematic available here: http://fisherconsoles.com/service manuals/fisher executive ii 1000 st1000 sm.pdf If this unit came from somewhere in the Chicago area it might be the sad outcome of this fiasco: http://www.audiokarma.org/forums/index.php?threads/anyone-know-what-model-this-is.787748/ No matter its origin, it means somebody cannibalized one of Fisher's rarest and, arguably, finest consoles. The Karma here is that it was designed to operate in conjunction with the control amp to which it connected via an umbilical; so it would need to be modified to operate as a stand-alone amp - unless it comes with it. And there were other unique components associated with this console such as the timer mechanism. I would think this is one of the rare instances where the value of the individual components ought to be less than the console whole.
     
  16. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Red is absolutely correct as to the designation of this amplifier belonging to the Executive (Model 1000) and Executive II (Model St-1000). One other telltale clue as to this amplifier's origin versus the more common SA-16, is that this amplifier uses the smaller (and lighter duty) 6V4/EZ80 rectifier tubes (consistent with these Executive consoles), while the SA-16 uses the heavier duty 6CA4/EZ81. This leaves little doubt that the Model 1000 amplifier predates the SA-16, with the SA-16 being the natural evolution of the Model 1000.

    In comparing the two amplifiers, the Model 1000 amplifier by design could be called a blue collar design, lacking clear refinements of the SA-16. As mentioned earlier, the 1000 amplifier lacks the usual Fisher stereo component accoutrements of a full compliment of output taps and AC Balance controls, and is also rather (shudder) Magnavox in it's basic design constraints. Consider:

    1. The output tubes are not driven very hard in this design, which will yield a long life for them. At a quiescent current of 30 mA per tube, they operate at about 9 watts plate dissipation each (or just 75% of the conservative Design Center rating system used at the time), but also only produces about 9 watts at best per channel as well with both channels driven.

    2. The level of NFB employed calculates to just 9 db, which is quite typical of mid-grade console design.

    Now the driver stage design and OPT used are both very decidedly well above that of Magnavox EL84 designs, but the penalty of Fisher's driver stage design is the rather low sensitivity it produces (2.0 vac per channel required for full power output in the Model 1000). Magnavox, squeezing out every last oz of functional capability from its designs, used a paraphase style phase inverter that has much more gain (typically requiring less than 1 volt for power) than Fisher's cathodyne design, but also has much poorer AC push-pull balance across the audio spectrum (and therefore higher distortion). However, since Fisher was using this amplifier with a significantly better control preamp than Magnavox ever used, the high input level requirement of the Model 1000 was not a concern in the overall design of the Executive. Magnavox -- often using no more than passive tone controls between a high output crystal phono cartridge and their power amplifiers, needed as much sensitivity as they could squeeze out of their amplifiers. Ergo, performance was sacrificed for sensitivity in their designs.

    By comparison, the SA-16 comes off as a hot-rodded Model 1000:

    1. Output tube screen grid voltage is increased so that full power output with both channels driven now crosses the magic 20 watt barrier at 11.5 watts per channel.

    2. Output tube quiescent current is increased notably to 38 mA per tube, with each tube now operating at just over 11.9 watts plate dissipation, or nearly at 100% of the 12 watt Design Center rating for these tubes. Still, by the more modern yet Design Maximum rating system, the tubes in this design are operating at about 83% of their maximum rating under this system (14.4 watts), so the design is hardly considered to be poor engineering practice. Rather, it just shows how conservatively they are operated in the Model 1000 amplifier by comparison (under 64% of dissipation rating using the DM rating).

    These bump ups in output tube operating levels were necessary to both bump up power, and bump down distortion in the SA-16, versus that produced by the Model 1000.

    3. With the change to a 12AX7 driver tube, NFB was nearly doubled to 17 db (yielding a 2.5X improvement in damping and distortion), and importantly, greatly improved the input sensitivity to just .85 vac required in each channel for full power output. This then required the use of input level controls to tame the hot sensitivity as necessary, but most importantly, allowed the SA-16 to be used in a variety of applications since its input sensitivity could be tailored to suit.

    With the output tubes producing more power at lower distortion, more NFB employed, and AC Balance controls added to optimize the lower distortion possibilities, the SA-16 is a Model 1000 all grown up, leaving anything resembling a Magnavox design in the dust, and moves this design topology closer yet to Fisher's ultimate execution of 6BQ5 tube class design: The SA-100. While the SA-16 a significant step above the Model 1000, the SA-100 is a serious step yet above the SA-16, with full AC and DC Bias and Balance controls, fixed bias operation, passive regulation of output tube screen grid voltage, and seriously hefty OPTs.

    An interesting observation is that in comparing the Model 1000 and SA-16, the Model 1000 uses the exact same output transformer as used in the mid-version 30-A mono amplifier (also the same as used in the Medalist Series II R-20 receiver), identified by its 8 and 16Ω only output taps, while the SA-16 uses the same OPT as used in the last version of the 30-A amplifier, with its full 4,8, and 16Ω taps. Using a 12AX7 driver tube in all versions of the 30A however, it has many of the benefits obtained by switching to that tube for driver service in the SA-16 from the 12AU7 of the Model 1000 design as well.

    I hope this helps!

    Dave
     
    Last edited: Nov 10, 2018

     

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  17. TheRed1

    TheRed1 Console Conservationist

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    Thanks, Dave. The amount of information you are able to glean from a schematic always amazes me - to say nothing of putting it into its historical context. The Magnavox comparison is very interesting. I have always suspected that this particular chassis may have been one of the first new designs after Fred Mergner took over from George Maerkle as Fisher's chief engineer. Since Mergner and many - if not all - of the "Dutchmen" had been lured away from Grundig, I'd be curious how the "1000" compares to Grundig's designs from the mid 1950's. Was post-war German hi-fi design philosophy similarly conservative to Magnavox? I would think so but have no evidence to support that hypothesis.
     
  18. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Thanks Carter -- I don't have any input to offer about Grundig designs, but regardless, I think you may very well be right about the 1000 being at least near the jumping on point for the Dutchmen. The 1000 was not unique in being an stereo design or that it used small bottle output tubes as all manufacturers were moving in that direction at the time as part of the natural evolution of technology. It wasn't even unique in being a console only design, as Fisher had done that before with at least their model 24 console. What I see as significant at the time, was the very decisive shift towards performance from a small foot print.

    Maerkle's time at Fisher produced cost-no-object large foot print pieces. They were unique for sure, but that would be expected because if Fisher was anything, he was innovative. So I think the general innovative direction always came from Fisher, while Maerkle executed that directive in his own unique style, with large chassis pieces using massive transformers and non-traditional designs. With the coming of stereo however, downsizing the foot print became imperative if Fisher equipment was to retain any kind of WAF in living rooms across the nation. But downsizing while retaining high performance was not an easy thing to do in that day, as typified by the performance of the Model 1000, and its resulting performance comparison to Magnavox. Engineering efforts like the Model 1000 likely left Maerkle feeling like a fish out of water: gone was the cost-no-object approach using mass to impress and uniquity of design to intrigue. For someone who created the completely unique 50A series of amplifiers and all their offspring, developing the Model 1000 must have been an exercise in drudgery.

    Therefore, I think it's highly possible that the Model 1000 was actually a Maerkle effort, that Mergner and company then got a hold of, and transformed into the SA-16. Consider that in the time between the Model 1000 and the SA-16, there were no technological improvements to cause the performance increase of the SA-16 over the Model 1000; there was just improved execution of the same basic topology. If that's the case, then why not just start with the SA-16 to begin with -- unless fresh thinking separates the two units in the form of Mergner coming in to take over. Other things support the change in regime between these two units as well, which start with little things like a different approach to designating model numbers, different symbols used and information shown on the relevant schematics, and expanded usable tube designations as mentioned earlier.

    So I think the case can be made that the Model 1000 is the peg in the ground after which the Mergner influence became the driving engineering force at Fisher, that carried them into the heady days of early stereo, and beyond throughout their phenomenal successes of the 1960's.

    Dave
     
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  19. Tim D

    Tim D AK Subscriber Subscriber

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    Nice piece Dave. Very nice.
     
  20. lilwing

    lilwing CAGE FREE AUDIO ZOO Subscriber

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    I've had this for a while:
     

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