Herb Reichert's tube manifesto

Discussion in 'General Audio Discussion' started by rlow, Jun 28, 2018.

Tags:
  1. ultrabike

    ultrabike Measurbator - Admin

    Staff Member Pyrate MZR
    Joined:
    Sep 25, 2015
    Likes Received:
    8,960
    Trophy Points:
    113
    Location:
    Irvine CA
    I would love to see a 200W/channel Class A pure tube amp (no hybrids) for dynamic drivers with shit tons of feedback, w/o the need to rewire your power grid, and that would inconspicuously fit in your average SoCal condo.
     
    Last edited: Jul 19, 2018
  2. Armaegis

    Armaegis Friend

    Pyrate BWC
    Joined:
    Sep 27, 2015
    Likes Received:
    7,466
    Trophy Points:
    113
    Location:
    Winnipeg
    I'm surprised there isn't a hifi heat pump to reclaim all that waste energy to... I dunno, power your wine cooler or something. Maybe heat up the kiddie pool.

    edit: actually, using that to warm up a recovery tank before your water heater wouldn't be that bad of an idea either
     
  3. ultrabike

    ultrabike Measurbator - Admin

    Staff Member Pyrate MZR
    Joined:
    Sep 25, 2015
    Likes Received:
    8,960
    Trophy Points:
    113
    Location:
    Irvine CA
    Class A 200W/channel SET amplifier w 100 dB of unicorn global feedback.

    Make Global Warming Great Again.
     
    Last edited: Jul 19, 2018
  4. trung225

    trung225 Facebook Friend

    Joined:
    Oct 22, 2015
    Likes Received:
    123
    Trophy Points:
    43
    200W for Class A SET Amp doesn't exist, at least yet. But I have heard a 120W one, the NAT Transmitter. If you can make a PSE version of it, you will have 240W. The electricity bills will be ridiculous, of course, and I'm sure your wife/gf will be mad at you :D
     
  5. ultrabike

    ultrabike Measurbator - Admin

    Staff Member Pyrate MZR
    Joined:
    Sep 25, 2015
    Likes Received:
    8,960
    Trophy Points:
    113
    Location:
    Irvine CA
    But can it be done w 100 dB of unicorn negative feedback?
     
  6. trung225

    trung225 Facebook Friend

    Joined:
    Oct 22, 2015
    Likes Received:
    123
    Trophy Points:
    43
    Oh, I forgot the later requirement. The NAT one is zero feedback.
     
  7. ultrabike

    ultrabike Measurbator - Admin

    Staff Member Pyrate MZR
    Joined:
    Sep 25, 2015
    Likes Received:
    8,960
    Trophy Points:
    113
    Location:
    Irvine CA
    My point is this:

    I don't see the need to bring Child's Abuse Laws or Mott Gurney's electron/hole speed rape theories. Nor discussions about n (negative) and p (positive) skinny dipping of silicon in transistor boobs.

    While I'm not the foremost expert in tube amplifier designs, it is my understanding that many tube amplifiers have less open loop gain than many "SS" operational amplifiers. High open loop gain seems desirable for high negative feedback, which reduces distortion.

    All that said, there seem to be Triode designs that do incorporate negative feedback to mitigate distortion (on top of Triode's intrinsic feedback):
    http://www.valvewizard.co.uk/localfeedback.html

    Different technologies likely have different strengths and may even target different random requirements. One uses such strengths to make the best of it. There is no need to get religious about it, or go crazy about the equations. One likes what one likes. And life is good.
     
    Last edited: Jul 20, 2018
  8. Dzerh

    Dzerh Friend

    Pyrate
    Joined:
    Apr 1, 2018
    Likes Received:
    425
    Trophy Points:
    63
    Location:
    San Ramon, CA, US
    I believe Child and Mott were brought just in response to my question about linearity of basic devices - transistors and tubes, outside of actual amps designs.
     
  9. sodacose

    sodacose MOT: WTFAmps

    Joined:
    Feb 3, 2017
    Likes Received:
    47
    Trophy Points:
    18
    Location:
    Wisconsin
    Home Page:
    Where is the 200W Class A single ended transistor amp? My point is that this is a question of topology, not device.

    Solid state has an advantage when it comes high open loop gain: the N and P channel types simplify direct coupling which is required to apply high amounts of feedback and maintain phase stability. This has lead to a trend towards high feedback compound amps.

    But that doesn't mean tubes cannot achieve high open loop gain (Williamson, Dynaco, et al). We don't see high open loop gain often though because the trend in tube amplification is no feedback and the monotonic decay distortion profile (and high open loop gain would be unnecessary for these ends).

    Designers are going to exploit the advantage and minimize the weakness of whatever device they use. The trends that result are just trends, not rules.

    I'm in total agreement on this. Understanding some of the science behind the hobby is necessary for us to avoid making it into a religion. That's all I aimed to add to the discussion.
     
    Last edited: Jul 20, 2018
  10. ultrabike

    ultrabike Measurbator - Admin

    Staff Member Pyrate MZR
    Joined:
    Sep 25, 2015
    Likes Received:
    8,960
    Trophy Points:
    113
    Location:
    Irvine CA
    I think it's a question of both topology and device.

    It is my understanding that with high open loop gain, afforded by some "SS" devices, one may be able to achieve more than 200W somewhat efficiently using a Class AB topology by applying negative feedback to keep distortion relatively low.

    Let's relax things a bit with the Class A topology. Do you know of a tube amp (non-hybrid) that can achieve more than 200W using a Class AB topology and negative feedback with very low distortion? Are there vacuum tubes than can support this currently?

    I think high voltage outputs are easier with simple tube devices than with simple "SS" devices, but high output currents are more problematic for most tube devices, which limits the amount of power delivered to low impedance dynamic drivers. Is that not a true statement?

    You are talking about trends that are not bound by rules. I feel devices have their limits and their strengths. And those strengths and weaknesses result in more than just trends. I think they result in a set of design rules. One maybe able to get creative and come up with something new, but all with in the constraints of what a device can do.
     
    Last edited: Jul 20, 2018
  11. sodacose

    sodacose MOT: WTFAmps

    Joined:
    Feb 3, 2017
    Likes Received:
    47
    Trophy Points:
    18
    Location:
    Wisconsin
    Home Page:
    Audio Research Reference series has more than one, Rogue Audio Apollos, McIntosh MC2301. These mostly use KT88/KT120/KT150 or variants. Class AB and feedback are techniques that originated with tubes, though transistors have successfully taken the approach much further.

    Tubes create power with large voltage swing while transistors create power with large current swing. Power is current times voltage. To drive a low impedance load, most tube topologies use transformers to convert high voltage low current to low voltage high current. Early transistor amplifiers also used output transformers. Output transformers are not perfect and that's a point of weakness in many tube topologies (and the weakness should be weighed against strengths).

    Tubes and transistors have electrical/mechanical limits and I don't mean to imply otherwise. I think we are using the same terms in different ways. Designers cannot violate the limits of a device, of course. By 'trends, not rules' I'm referring to what topologies the respective devices can and can't be used for. There are no such hard limitations, but there is good sense guided by relevant strengths and weakness. Like you said, topology has as much to do with the story as device.

    I am not the personal emissary for vacuum tubes, by the way. I won't claim that they are universally superior to transistors just as I won't claim the opposite. The best tool for the job starts with the goals and task at hand (and subjectivity quickly takes over from there).
     

Share This Page