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Using standard 50/60hz transformer as output transformer

Discussion in 'Electronic Design' started by powerampfreak, Apr 1, 2007.

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  1. Hi,
    Is it technically possible to use a "standard" 230Vac to 24Vac (for
    example) as an output transformer in a tube circuit?
    Regards
     
  2. Only if you don't much care about the audio.
     
  3. It will probably work at 50/60 cycles, but take the feedback from the
    secondary for audiophile performance.


    martin
     
  4. I have actually tried this in my school days or there about.
    As those transformers have no air gap, you need an old tube type
    one with 2 HV windings, say 220V to 300 + 300 + 6.3, and
    then use a _balanced_ circuit (as used for dual anode rectifiers).
    It worked, but not very good, but my impedance matching was likely not ideal.
    Probably it is not really the sort of iron for HiFi too (high frequency losses).
    Perhaps you could use a 220V transformer with a 110V tap....

    Better is to forget tubes and output transformers, build a transistor amplifier.

    Or you could wind your own transformer.
    Actually, on the subject of amplifiers and transformers, I bought a McCrypt
    PA3000 power amplifier from www.conrad.nl, for _69,95_ Euro:) (say 100$).
    It has in it a 200W ring core transformer, 2 SEPP transistor output stages
    with 16A transistors, delivers easily 100W sine per channel, has XLR and phone
    input, has a temp controlled fan, has a 19inch housing with grips, has separate
    volume controls for left and right, real mains switch....
    If you add up the component prices it is impossible.
    So I have given up now on audio amp design.
    It says designed in Germany, but I suspect it is build in China.

    It is so powerful that I have not run this one at 100% yet (oh yes it has
    warning LEDS for clipping), have blown enough speakers the last few years.

    BTW this is only for the REAR channels in 5.1
    LOL
    Can you do it for 100$?

    I would not have written this if I had not fallen for the April 1 joke 'made millions in
    electronics ;-( ).
     
  5. John  Larkin

    John Larkin Guest

    It will certainly work, but you'll get some high-end rolloff from eddy
    current effects. And don't go single-ended class A, or it could
    saturate; these transformers aren't designed for DC in the windings.

    Hey, lash up a breadboard and try it! Tell us how it sounds.

    John
     
  6. Tim Williams

    Tim Williams Guest

  7. Eeyore

    Eeyore Guest

    I'm sure it'll be fine at 50/60Hz !

    Graham
     
  8. I made an output stage with a pair of triodes and a small EI
    power transformer with dual primaries, and it had pretty
    fair fidelity up to about 3 kHz, so AM radio would sound
    fine through it. I am sure a toroidal power transformer
    would work even better.
     
  9. .... especially if you want to take the audio all the way
    down to 20 Hz. You might take two of them and wire one of
    the primaries from each in series but wire the secondaries
    in parallel. Toroids are easy to stack, too.
     
  10. Oh, another thing, This trick gives you something like
    screen taps, too.
     
  11. Phil Allison

    Phil Allison Guest

    "powerampfreak"

    ** Go search the archives " rec.audio.tubes "

    Toroidals with twin primaries of 120/120 are so usable.



    ........ Phil
     
  12. Phil Allison

    Phil Allison Guest

    "John Popelish"


    ** Mains toroidals often have a flat response to 100 kHz and beyond.

    Virtually no magnetising current to cause distortion.

    Only issue is that 120 volts rms per side at 50Hz may not be enough.



    ........ Phil
     
  13. Phil Allison

    Phil Allison Guest

    "John Popelish"

    ** That is a silly myth - you never need full power output at 20Hz or
    anything near it.

    A toroidal tranny that begins to saturate at say 130 volts at 50Hz will be
    able to accept 65 volts at 25 Hz.



    ** Nice idea.


    ......... Phil
     
  14. Eeyore

    Eeyore Guest

    I suppose you've never heard any drum 'n bass style music then ?

    Graham
     
  15. Phil Allison

    Phil Allison Guest

    "Eeysore =ASD fucked pommy IDIOT "



    ** **** off - you asinine tenth wit cretin.



    ....... Phil
     

  16. For your information, I'm working at a audio power amp manufacturer,
    only transistor designs though, but our biggest unit produce over 12kW
    as a stereo amp.
    My interest around tube designs has developed lately since I like to
    build a tube amp myself... Try something I never did before.
     

  17. We're not talking about Hi-Fi here, just for guitar amp purposes, then
    you won't need a very broad audio range, maybe 50hz up to 5khz or
    something.
     
  18. Phil Allison

    Phil Allison Guest

    "powerampfreak"
    "Phil Allison"

    ** We were not talking to you - FUCKWIT !!!




    ......... Phil
     
  19. It is possible; but the quality will never be anywhere near as good as
    even the most basic purpose-designed item. When designing a valve
    output transformer you need to be able to optimise:

    1) The turns ratio

    2) The core losses and copper losses

    3) The coupling between primary and secondary over a wide range of
    frequencies.

    4) The self-capacitance of the primary.


    With an off-the-shelf mains transformer,

    1) Will be fixed and if you are lucky it may be somewhere near what you
    want (but it more likely will not). If it is wrong, you will prevent
    the output stage from delivering its full power into the load. You may
    also get flashover inside the windings or across the pins of the
    valveholder.

    2) Will be optimised for full load 50 c/s operation and will be nothing
    like what you want. The core may run into saturation if you try to use
    it at full power below 50 c/s; and this could damage the valves.

    3) Is determined by the quality of the core material at medium
    frequencies and by the configuration of the windings at high
    frequencies. You can get away with power-grade laminations for
    moderately demanding audio purposes (I have done so many times); but
    audio grade will be better if you want low losses.

    The windings need to be split into sections and interleaved, this is a
    complex process which was well-understood by the 1930s, so you need to
    read a designers' handbook from that era if you want to do it correctly.

    The limitation placed on your frequency response can be partially
    covered-up by negative feedback, but the losses due to poor coupling
    cannot be overcome in this way.

    4) Will set a limit to how much feedback you can use before it becomes
    unstable. Phase shifts are caused by the self-capacitance of the
    windings interacting with their inductance. Because of the large number
    of turns of fine wire on the primary, valve designs become unstable at
    lower frequencies and with far less feedback than transistorised
    transformer designs (which need fewer turns). Even medium-quality
    purpose-built valve output transformers are quite limited in the amount
    of feedback they will allow, and mains transformers will be very limited
    indeed.


    Try it, have fun ...but don't expect miracles.

    P.S. Always keep one hand in your back pocket when you work with live
    valve equipment, it prevents an electric shock from travelling straight
    across your chest and stopping your heart.
     
  20. We?

    How many do you speak for?

    How do I make sure I'm not one of them?
     
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