Output Transformers

Discussion in 'Home Theater Projects' started by ChristopherDAC, Feb 25, 2004.

  1. ChristopherDAC

    ChristopherDAC Producer

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    I am considering constructing a multichannel amplifier using thermionic valves for amplification. Unfortunately, to match the high output impedance of these devices to the low input impedance of the ordinary speaker, the use of a transformer usually indicated -- and as tube amps have grown rare, transformers with the required characteristics [broad frequency response, &c.] have also become unavailable. I would really rather not buy defunct old tube amps and tear them down for their output transformers, particularly since they might not quite match contemporary ideas of "high fidelity" and could quite easily be full of PCBs and other toxins. Likewise, I am not certain that I would have much success winding my own. Has anyone any experience with this type of project? I do not want to commit any resources to it until I'm sure it can be done. On a side note, has anyone used transformers for matching an 8ohm amplifier to a 2ohm subwoofer, or anything of that kind? I notice that power losses from impedance mismatch show up as some people's major concern, and that is one solution.
    Thank you.
     
  2. Bob K

    Bob K Stunt Coordinator

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    Christopher,

    I am a tube nut, but even I use dreaded ss amps for home theater. If you have a mixed music/ht system, I would suggest that, at most, you use a tube amp or amps for the two front channels and ss for the center and rears.

    If you want to go this route, I would not tear apart old tube amps for the output transformers. Many speakers with reasonably high sensitivity and benign impedance curves can be driven to high levels with, say, a 40W pp amp. I don't use them in my ht, but I have a pair of Pi Speakers Theater 4s (high 90's dB sensitivity) that would probably be quite good in that role -- I drive them to high levels with 8W 300B SETs. http://www.pispeakers.com I've hooked them up to a 40W EL34 pp amp and can blast people out of the house.

    Tubes amps are less rare than you think. You can get an old Dynaco on ebay (and there are kits to modify them, replace old caps, etc.), and modern manufacturers of high power amps (including amps that generate far more than 40W) include Conrad-Johnson, Manley, VTL . . .

    BTW, output transformers are not full of pcbs, so don't worry about that!

    Gotta get to work!

    Tempest Construction Pix: http://www.audiocircle.com/circles/m...view_album.php
     
  3. Robert AG

    Robert AG Stunt Coordinator

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    This magazine has tons of ads and info on manufacturers of new output transformers and associated parts. There are actually quite a few companies making them!

    www.vacuumtube.com

    I use tubes for my front L,C,R speakers in an active bi-amped configuration. I use solid state for the side and rear surrounds (7.1). Tubes are not only practical for home theater, but they sound fantastic. They can tame the otherwise harsh sound on some movies too.
     

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