Single Ended Output transformer question...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dumbell78, Feb 7, 2012.

  1. dumbell78

    dumbell78 Member

    Messages:
    4,578
    Joined:
    Apr 23, 2008
    Location:
    Sydney by way of Muddy Water Land (Chicago)
    Just wondering what you guys recommend for a OT in a Mini Plexi type of circuit? Kicking around the idea of building a mini plexi type of circuit and run any octal power tube. Probably use the Epiphone Valve Junior chassis as a platform.
     
  2. 5992

    5992 Member

    Messages:
    2,480
    Joined:
    Dec 9, 2005
    For circuits like this, I usually use a Hammond 125ESE. The primary can be configured for use with several octal power tubes: I've used 6V6, 6L6, EL34 and I've even used a 6550. Sounds good using an EL84, although it isn't an octal.
     
  3. gldtp99

    gldtp99 Member

    Messages:
    2,503
    Joined:
    Dec 23, 2005
    Location:
    Texas
    for cost-effective experiments MPS iron works well---- i've used their stuff in several very good sounding push/pull builds-----i have two 10 watt SE OT's on hand that i haven't used yet.

    http://www.musicalpowersupplies.com/2.html
     
  4. alexandergj

    alexandergj Member

    Messages:
    96
    Joined:
    Oct 9, 2007
    Location:
    Leeds UK
    yes, 125ESE was regularly recommended for this application when valve junior modding was all the rage.
     
  5. dumbell78

    dumbell78 Member

    Messages:
    4,578
    Joined:
    Apr 23, 2008
    Location:
    Sydney by way of Muddy Water Land (Chicago)
    Thanks for the suggestions guys.
     
  6. 19181911

    19181911 Senior Member

    Messages:
    842
    Joined:
    Oct 12, 2011
    Location:
    USA2012ABO
    You could use a 50 watt push pull OT, just cap off the center tap on the primary...
     
  7. Trout

    Trout Member

    Messages:
    7,576
    Joined:
    Jun 23, 2006
    Location:
    Illinois/Far West Burbia
    I doubt most PP transformers are gapped properly for SE use, work? yeah, But correctly? not likely.
     
  8. Keyser Soze

    Keyser Soze Member

    Messages:
    1,477
    Joined:
    Dec 14, 2008
    Location:
    Johnson city, TN
    IIRC Hammond used to market one of their OTs as 'universal' - suitable for either SE or PP, but then stopped making such claims due to dissatisfaction over performance.

    But, 'proper' is also a relative term, particularly in the case of a low power SE amp, where the builder may want a core that quickly reaches saturation.
     
  9. dumbell78

    dumbell78 Member

    Messages:
    4,578
    Joined:
    Apr 23, 2008
    Location:
    Sydney by way of Muddy Water Land (Chicago)
    That is an interesting approach, I have never heard of that.

     
  10. 5992

    5992 Member

    Messages:
    2,480
    Joined:
    Dec 9, 2005
    Yeah, the Hammond 125A-125E series. I have a few of these. They suck for SE but actually sound pretty good for push pull operation. The main selling point for these is that they can be configured for a wide variety of primaries and secondaries. The are good for experimenting with oddball tubes the may need a different primary than most of the common 6V6/6L6/EL84/EL34 guitar tubes.
     
  11. 19181911

    19181911 Senior Member

    Messages:
    842
    Joined:
    Oct 12, 2011
    Location:
    USA2012ABO
    I forget the designer/amp, but there used to be a 10 watt SE amp that used a 50 push pull OT... From what I remember they sounded awesome.

    I've used a 50 watt bassman replacement OT in a SE EL84 prototype that rocked.
     
  12. 19181911

    19181911 Senior Member

    Messages:
    842
    Joined:
    Oct 12, 2011
    Location:
    USA2012ABO
    It was ADA, their A10 amp designed by Curt Emory, that is where I got the idea to try the big push-pull OT in SE operation. THe A10 used a 50 watt pp OT in SE.
     
  13. Ronsonic

    Ronsonic Member

    Messages:
    3,313
    Joined:
    May 14, 2006
    Location:
    Sunny Tampa, Florida
    They aren't correct, but there's so much more iron there that it won't saturate in this application.

    They can also be disassembled and reassembled with an air gap.
     
  14. EFK

    EFK Supporting Member

    Messages:
    1,023
    Joined:
    Jan 18, 2009
    "They can also be disassembled and reassembled with an air gap."

    I've read this a number of times and understand how it could be done fairly easily, especially useful if you have old or excess OTs sitting around. BUT! It seems like it would be a real bitch trying to break apart all the laminates once they've been potted and baked. They're practically welded together. Any simple way around that?
     
  15. Ronsonic

    Ronsonic Member

    Messages:
    3,313
    Joined:
    May 14, 2006
    Location:
    Sunny Tampa, Florida
    Some come apart pretty easily. Some. I've done those, and the others I've walked away from and kept for some other project. Really depends on the manufacturer, some do a varnish dip that's like they're welded, others come right apart after you knock loose the ends.
     
  16. donnyjaguar

    donnyjaguar Member

    Messages:
    4,243
    Joined:
    Nov 4, 2005
    Location:
    Canada
    You can use a PP transformer for SE work. Just load down the unused primary side with the same idle current as your output tube. This should stop the core from saturating. Not very efficient as you can imagine.
     

Share This Page