Supratek 845 PP crazy big 14 tube stereo amp anybody?

Discussion in 'Audio Hardware' started by Marsman, Mar 29, 2019.

  1. Bill Hart

    Bill Hart Forum Resident

    Location:
    Austin
    I have the original Quad II amps that I use with my old Quads (all restored)> They have almost no power for a normal speaker, but with the original Quad ESL they are perfect, better than the various ARC tube amps I used over the years with more power. I've got good glass in the Quad amps. They are very simple. I honestly never paid much attention to the circuit or what class they ran in; having them refreshed and putting GEC KT 66s in (which are probably worth more than the amps) made a huge difference in how they play.
    Very post war British industrial.
     
  2. vinylkid58

    vinylkid58 Forum Resident

    Location:
    Victoria, B.C.
    You're lucky to have those tubes. Had the opportunity to buy NOS GEC KT66's a few months back from a local seller, but just couldn't open my wallet that far.:cry:

    Always liked the "look". Might build look-alike amps with different tubes.

    jeff
     
  3. SandAndGlass

    SandAndGlass Twilight Forum Resident

    It is good to know that this SS circuit can operate as class "A".

    After my previous post, I was thinking that there are some modern SS amps that would operate at lower power levels in class A. The amps themselves were more powerful and beyond a certain power level, they moved into class A/B.

    I have no idea how they accomplish this, circuit wise.

    A few years ago, Emotiva make an XPA-1L, a 250-Watt monoblock power amplifier that did this.

    [​IMG]

    You could run it in the class "A" mode. When you did this, the first 35-Watts would be in class "A" and then it would switch over interaly to class A/B operation, or you could run it as a class A/B amp.

    I meant to buy a pair of these to check them out, as it seemed to be a good idea, but they discontinued the amp for some reason, when they brought out their generation 2 amplifier line.

    Here is a review from The Poor Audiophile web site about the XPA-1L.

    In the review, they do mentions some other brands of SS amps, which can be biased to run in class "A".

    The reviewer does note that you would be hard pressed to tell the difference between A/AB operation.

    I don't particularly see the point in class "A" SS amplifier's. I have little actual experience in this area and have not heard some of the high end SS class "A" amps, but I don't think that SS class "A" sounds anything like a class "A tube amplifier.

    In addition, SS amplifier's that produce any amount of class "A" power are heavy, expensive, consume a lot of power and generate a lot of heat.
     
  4. Roger Beltmann

    Roger Beltmann Old...But not obsolete

    Location:
    helenville, wi.
    My apologies to Jeff. There actually are class A push/pull designs. Class A definition says that plate current flows the entire 360 degrees. However, what if we use a phase inverter to get equal but opposite drive to the output tubes? When one tube is near saturation the other tube will be near cutoff. Power output is doubled and second order distortion is gone. However they require a special type of output transformer and a phase inversion stage. I could not find an actual production model but I did study some design schematics. Appears they would run quite hot. Once again apologies to Jeff.
     
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  5. vinylkid58

    vinylkid58 Forum Resident

    Location:
    Victoria, B.C.
    Apologies gladly accepted.:)

    jeff
     
  6. Ralph Karsten

    Ralph Karsten Forum Resident

    Location:
    St. Paul MN
    Class A has nothing to do with whether its push-pull or single-ended. Usually single ended circuits are class A (some radio circuits are class C). Push-pull can be class A, A2, A3, AB1, AB2, B and D. We've been making class A triode output transformerless tube amps for years. I get a lot of pushback on this topic; class of operation has a lot to do with how the tube is biased rather than anything else.

    The amp in question is a push-pull output with single-ended input.
     
    HiFi Guy likes this.
  7. Ralph Karsten

    Ralph Karsten Forum Resident

    Location:
    St. Paul MN
    Power output is a bit more than doubled even when class A. Push-pull is a lot more efficient. Also, to clarify, even ordered harmonics are cancelled in the output section, but if a 2nd order is generated elsewhere in the amp then that is still there. The output transformer is not that special- chances are good this one was available off-the-shelf from one of many manufacturers.
     
  8. SandAndGlass

    SandAndGlass Twilight Forum Resident

    This means what exactly?

    Are you saying that this is a class "A" amp?
     
  9. bluemooze

    bluemooze Forum Resident

    Location:
    Frenchtown NJ USA
    SandAndGlass likes this.
  10. Ralph Karsten

    Ralph Karsten Forum Resident

    Location:
    St. Paul MN
    It could well be. Can't really tell without some idea of the plate voltage and how much current is going through the tubes at idle. Apparently Mike Maloney was actually the designer/builder (if I read that correctly on this thread earlier)? If Mike says it was class A then that is probably true. I've known Mike a good long time; I don't think he'd be out to lunch on something like that.
     
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  11. SandAndGlass

    SandAndGlass Twilight Forum Resident

    Just have never been exposed to there off the wall designs, only conventional A and AB amps.

    Not familiar with the designs behind amps like class D, etc.
     
  12. Marsman

    Marsman Member Thread Starter

    Location:
    Plymouth MA
    If you guys are interested I will be posting the hand drawn schematic from Mick and maybe it will help you all understand the design I am not embarrassed to say this is all above my pay level
     

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