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Tube Amp Choices

Discussion in 'Amplifiers & Receivers' started by Zing, Oct 7, 2010.

  1. Zing

    Zing Retired Admin Famous

    If someone wants to look into Class A SET tube amps, what makes and models are available? The only one that fits this criteria and that immediately comes to mind is the Cary 805.

    I also thought of Jolida but they seem to specify "hybrid" for their amps which, I'm assuming, is some sort of cross between vacuum tube and solid state. And then of course there is McIntosh but they don't specify whether its output is Class A.
  2. soundhound

    soundhound Well-Known Member

    McIntosh is most definitely NOT class A, or anything close; they are near class B, which means that the output tubes are run near cut-off, and the distortion produced is "made up" for with high amounts of negative feedback, both global and local. They are the anti Christ of tube designs.

    While I don't have any specific model numbers to recommend, I would say that generally you want to stay away from hybrid amps, or amps which use "improvements" to the basic, classic design of a class A SET amplifier, which is in its self very simple and rather crude with few parts, but that's why they sound so good. This also goes for push-pull class A amplifiers (those over about 7 watts), because by the nature of the push pull output stage, even order harmonic distortion is largely cancelled, leaving only the odd harmonics.

    The only thing solid state I would tolerate in a class A SET amplifier is the DC power rectifier(s).

    If you're going to the trouble of buying a class A SET amplifier, you might as well get the real deal.
  3. Zing

    Zing Retired Admin Famous

    I was hoping you'd be able to throw a few names into the ring to increase the choices. The Cary 805 seems to be the one to have but, at $6500/ea, I'm guessing it'll remain on most people's wish lists.

    I know there are kits available (Dynaco perhaps?) but I was curious about the manufactured amps first. Apparently the high cost and limited options are what makes the kits so attractive to so many people.
  4. soundhound

    soundhound Well-Known Member

    Sorry, but I just haven't been in the market for a class A SET amp for years, so there's no reason for me to keep up on what's available.

    Dynaco does not make class A SET amps; they are all Ultralinear class A/B. They are a good choice however if that's the kind of amp you want. I use Dyanaco MKIIIs (somewhat modified) for my woofers (100Hz to 500Hz).
  5. DIYer

    DIYer Well-Known Member Famous

    Zing, ask PaulyT. He was building a nice DIY SET amp but it seems like he isn't using it. Maybe if the price is right... ;)
  6. Zing

    Zing Retired Admin Famous

    :laughing-rolling: That's classic! You really need to make a signature out of that.

    I can see it now...

    McIntosh - The Antichrist of tube designs.
  7. Vinyl

    Vinyl Active Member

  8. DIYer

    DIYer Well-Known Member Famous

    Zing, this is SET tube amp I use and Pauly was building (not sure what became of it). If you can solder, it can be built for about 7% of Cary 805 price. How does it sound? Excellent and noise floor is very low for SET amp which is essential for high efficiency speakers.
  9. PaulyT

    PaulyT Behind the Curtain Staff Member Administrator Moderator Superstar

    Yeah, I've got it assembled and working on the workbench, I just haven't put it in its enclosure yet.
  10. Aaron German

    Aaron German Active Member

    Man, that was a long time ago that you were at that stage. I can't see why it's not finished. It's not like you've been doing anything else.
  11. soundhound

    soundhound Well-Known Member

    Not to be contrary, but I personally would not choose that SET circuit, mainly for the inclusion of the solid state parts, particularly the 2SK2700 which is associated with the signal path to the output tube.
  12. DIYer

    DIYer Well-Known Member Famous

    For the price of this amp, the quietness is hard to beat. That 2SK2700 is MOSFET and here is a technical article on that particular design. It's too technical for me and possibly the same for many of us. :oops:
  13. soundhound

    soundhound Well-Known Member

    Actually, quietness, at least lack of hiss, is very easy to achieve in a SET design, considering that there are only two tubes and very few other parts (hum is always going to be a challenge in a SET, and this design is no different). The data sheet for the 2SK2700 is here: http://www.toshiba.com/taec/components2/Datasheet_Sync//77/3108.pdf.

    The design is, in my opinion and experience, trying to solve a problem which is not a problem, and making a circuit more complex than it needs to be.
  14. DIYer

    DIYer Well-Known Member Famous

    What I like about Tubelab SE is, fixed bias, DC filament heater, adaptability with different output tubes and transformers and one can do this at such a low cost. :handgestures-thumbup: It's got "Zing's first SET tube amp" written all over it. :eusa-clap:
  15. soundhound

    soundhound Well-Known Member

    That me be, but I would not recommend that design for the best sound quality available from an SET. Besides, how many times have you swapped out the output transformer? :teasing-tease:
  16. DIYer

    DIYer Well-Known Member Famous

    None so far but if I have money and time... :teasing-neener:
    Actually, what I meant by adaptability was, it allows one to have more choices when starting out than other SET amps I've seen. It can be built for around $350 up to whatever one desires depending on the price of transformers, capacitors, tubes and chassis.
  17. soundhound

    soundhound Well-Known Member

    Yes, but is potentially compromised sound quality worth all the customizing ability in the world? Not for me.

    Here is a schematic for a SET which does not have any solid state devices in the signal path: http://diyaudioprojects.com/Schematics/SE-2A3-Tube-Amp-Schematic.htm I'm sure there are others, but this came up on a quick Google search.
  18. DIYer

    DIYer Well-Known Member Famous

    I did build SET tube amp with 2A3 output tube and all tube components before but it was salvaged to make Tubelab SE so I didn't get to compare them side by side. I did measure the hum level at the speaker terminal though. 2A3 was 3mV and Tubelab SE is 1mV (as low as my multimeter can measure). If I can come up with enough money for another trip to LA next year, I'll have to bring my current SET amp over to your place and compare it if you desire. :think:
  19. soundhound

    soundhound Well-Known Member

    We could certainly do that comparison. It might be more revealing though to do a spectrum analysis of your SET (I have a professional level FFT program). If there's no audible or measurable difference between the two amps, I'd be glad to eat my words.

    Didn't you go with DC power on the output tube filaments with a switching supply? With the super efficient horns, its almost impossible to get the hum low enough without DC on the filaments.
  20. Zing

    Zing Retired Admin Famous

    I found another contender. :happy-smileygiantred:

    The $14K Ayon Thor. :angry-banghead:

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