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What tubes to use

Discussion in 'Electronic Repair' started by [email protected], May 12, 2007.

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  1. I want to build a tube power amp for my stereo. Tubes have always had
    the best sound. Actually two amps, one for each channel. First off,
    what tubes can I use in Push-Pull Parallel to achieve at least 1000
    watts RMS per channel. I want real power. Not peak to peak, but true
    RMS. Secondly, where can I obtain the output transformers, or will I
    have to have them custom made, and where?

    When I was much younger I had two amps that used 4 6L6 tubes in
    push-pull parallel and I was able to achieve about 120 watts per
    channel. The sound was great, but 6L6 tubes have their limits on
    power, and tend to be noisy (at least the old ones did, as I had to
    shock mount the amps to prevent feedback thru the tubes.

    Going with 1000 watts, I will need much more control and tubes that
    can handle the abuse. In reality, I'd like to go for 2500 or even
    5000 watts per channel, but I doubt any tubes can handle that.

    On the other hand. the thought arises to build 4 of these amps, use
    two for the low end, and the other two for the horns. I assume that
    for the horns I could cut back some on the power output, but need
    everything I can get for the bass end, since I intend to build a wall
    of 16 inch woofers.

    Thanks for all help.

    Mark
     
  2. Guest

    For that kind of power you will find it difficult, if not impossible,
    to achieve your goals. All kinds of things will be unobtainable at
    the extreem high power you are talking about..
    **output transformers.... for sure ... if you could get them they
    would weigh several hundred pounds each.

    **power transformers and power supply ... several amps at 800 - 1200
    volts or more ! ! expensive and hard to do.

    **output tubes... even with push pull- parrallel ( 4 tubes) you will
    have trouble getting anything close to 1000 watts with audiophile
    tubes. You would probably have to use really expensive RF power
    tubes which in all likely-hood will not be power pentodes and will
    require serious drive power which at your desired power level would be
    a problem for even "normal" high power audio output tubes.... then,
    where would you get the high power interstage transformers.

    All of these things will be most likely an exercise in futility.
    My advice to you is to stick with solid state for you desired very
    high power requirements.... there are several brands of readymade
    1000 watt plus (many units can be bridged to increase power)
    professional solid state amplifiers available that would be hard to
    beat the price even if you built it yourself.
    electricitym
     
  3. The main interest in valves these days is with SET (single ended
    transformer) designs which are the best for that 'valve sound'. And by
    nature low powered so need sensitive speakers.

    However, all is not lost. Simply use one of those driving a suitable
    inductive load then feeding a decent high power solid state design. The
    valve amp will give you all the distortion of the type you crave and the
    SS one amplify it.
     
  4. James Sweet

    James Sweet Guest

    Is this a joke? 1KW from a tube amp? What do you plan on using for output
    transformers? Hope you have a forklift to move them around and a very large
    electrical service to power it all. It would eliminate the need for central
    heating in your house as well.
     
  5. isw

    isw Guest

    It used to be done all the time. While in college, I babysat an RCA
    BTA-50F1 (almost the last of the plate-modulated 50 kilowatt AM
    transmitters). The modulator delivered a cool 25,000 watts of tolerably
    clean audio. The transmitter was on the second floor; the entire first
    floor was the plenum for the blowers.

    I suggest you look for a couple of old AM broadcast transmitters, and
    extract the modulation transformers and audio circuits, for a good
    starting place.

    Then, I suggest that you learn exactly what the performance differences
    are between tube and solid state amplifiers. Pay special attention to
    what those output transformers do to the frequency and phase response.

    Prepare to rewire your listening room, too, because if you don't,
    there's no way you're getting a kilowatt -- much less a stereo pair of
    kilowatts -- of output from a tube amp connected to a normal outlet.
    With a switchmode solid-state job and special attention to efficiency,
    maybe.

    Isaac
     
  6. No, not a joke. I have wanted all my life to build a stereo that
    handles the same power levels as a live concert. I'm now retired and
    want to finally do it. Back when I was in my 20's I built my rather
    crude system which consisted of 3 separate amplifiers, each putting
    out 120Watts RMS, with 4 6L6 tubes in PPP. (The 3rd amp was a
    "center" or combined channel that drove a bank of woofers). My huge
    speaker towers that I built with one inch thick plywood, held guitar
    amp speakers and horns. The power was amazing, but not quite as clean
    as I wanted it, and that feedback thru the tubes was always a problem.
    Once, when I was rather messed up (I'll skip the details), I cranked
    it wide open and blew all the windows out of my apartment (the
    landlord was NOT pleased). I attribute the window shattering to low
    end distortion, (in a much too small apartment).

    Now, I live on a farm and I want to fill the whole farm with
    "live-like" sound. I guess you could call it my personal "Woodstock"
    (ya, I'm showing my age). Actually handling hundred (or more) pound
    transformers/amps would not be a problem, since I actually DO have
    tractors and such to move them. but getting the xformers probably is.
    I have 400AMP service at my panel, so I got enough power too.

    However, I will consider using solid state amps if I can achieve the
    right sound. I would imagine I could get some ready made PA system
    amps. I used to know a guy that worked for a sound company that did
    all the sound for major rock concerts. I know for fact that they had
    the capability to run 10,000 watts total, and in most places used the
    full amount at outdoor concerts. So, myself wanting to run at least
    2000watts total is not too much to ask.

    I'm curious why you think this is a joke? I'm asking because there
    was a time when everything was tube. What did they use back then for
    large concerts and auditoriums for the main system? Ya, I know that
    the concerts back in those days were not as large as they have been
    since the late 60's. I'm curious what they used at Woodstock, since
    that was more or less the first concert of it's size, and that was
    during the transition from tube to semi-conductors, and I know that
    semi-con... power amps back in those days were prone to failure.

    There seems to be a lot of historical information about Woodstock and
    other major concerts back in the 60's and 70's, but finding details
    such as the type of power amps used to supply the main system just is
    not documented.

    Mark
     
  7. I'm not real familiar with this. Is there a website with details and
    possibly schematics or at least detailed drawings? This might be just
    what I am looking for.

    Thanks

    Mark
     
  8. James Sweet

    James Sweet Guest


    People get so caught up in watts these days, there's a lot more to audio
    than watts. Large concerts use(d) stacks of amplifiers to achieve the total
    power, you need a lot of power coupled to high efficiency speakers to fill
    an auditorium or outdoor area with high volume sound, but in your house? How
    much space do you have? I have an amp that produces a solid 120W RMS per
    channel connected to a pair of moderate efficiency speakers and it's capable
    of far higher volume than I would ever wish to listen to. You can get
    speakers that will produce enough sound to damage your hearing at 50W, or
    you can get them that will require 500W to produce the same volume, look at
    those first.

    100W is very large for a tube amp, 1KW is outlandish. If you still wish to
    proceed, you're asking the wrong group.
     
  9. No, they haven't. A crappy tube system sounds as bad as a crappy solid state
    system.
     
  10. Bill Janssen

    Bill Janssen Guest

    I suggest that you first go to a transformer manufacturer and get quotes
    on the output trans.

    A better idea is to build an amp. for each speaker.

    Bill K7NOM
     
  11. Eeyore

    Eeyore Guest

    Utter nonsense. First off you're got that sodding great lump of steel in the
    output transfomer which corrupts everything.

    Lateral Mosfets are the best by far.

    Graham
     
  12. Eeyore

    Eeyore Guest

    You mean the ones with the highest distortion !

    Graham
     
  13. Eeyore

    Eeyore Guest

    Yes. You can get SR (sound re-inforcement as it tends to be called these days
    rather than PA) amps with power rating up to about 10kW in a single unit these
    days.
    http://qscaudio.com/products/amps/powerlight3/powerlight3.htm

    They aren't designed to be ultra-hi-fi though. Their specs are good but the main
    criteria for SR use is power and light weight.

    You can however get very good studio monitor type amps of the 1kW / channel
    rating.

    Graham
     
  14. Eeyore

    Eeyore Guest

    Worse usually in fact.

    Graham
     
  15. That and poor damping factor.
     
  16. Eeyore

    Eeyore Guest

    That give that 'better' sound - LOL !

    Graham
     
  17. TMI

    TMI Guest

    Dear Mark,

    This topic comes up every so often. Today the cost is so prohibitive.
    Can you spend $20.00 per watt for parts? If not, better try solid
    state. Tubes are simply not available on demand and you will pay
    market price for what you can find. Assuming you can spend the money,
    take a serious look at the OTL designs of Futterman. They scale well
    and do not require an output transformer. Consider wiring your
    speakers in series or use custom voice coils so the load is 16 ohms or
    more. Eliminate all passive crossovers. Consider multiple amplifiers
    per frequency range. Reconsider the choice of speakers. Set an SPL
    goal-not a watts goal and work backwards.

    VTL labs made a 500 watt tube amp based on 6550s. The Mac MC3500 did
    500 watts midband on 6LF6s. You could strap 2 for a 1000 watt single
    channel.

    On the solid state front, a strapped Bryston 4b sounds fine. BGW has
    several offerings. Often, using solid state below 1khz and tube above
    is a better answer. There are real issues with power handling at high
    frequencies. Few drivers can take the power. Still fewer are worth
    listening to. If you use multiple drivers, just use multiple amps.
    There are real issues associated with the design of wideband, high
    power output transformers. <35 watts is relatively easy. At 60 watts
    it is difficult. Above 200 watts becomes rocket science.

    Tom
     
  18. The reason to use valves is to get that valve 'sound'. Eliminating some of
    the causes of the distortions so beloved of valve enthusiasts defeats the
    purpose.
     
  19. bz

    bz Guest

    Once you have a good amp, without distortion, it is relatively easy to
    modify the signal at a low level, to produce any kind of distortion you
    might want.

    Analogue to Digital(A-D) --> computer --> D-A --> AMP would allow you to
    produce a signal with almost any imaginable and certainly any 'real amp'
    characteristics that one might desire.



    --
    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
     
  20. You'd need to package it inside some large heavy box that glowed in the
    dark, though. Don't underestimate the power of the eyes over the ears.
     
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