1. The Rules have been updated regarding posting as a business on TGP. Thread with details here: Thread Here
    Dismiss Notice

Multipurpose OT/PT for amp prototyping?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Axeplyr, Jan 6, 2008.

  1. Axeplyr

    Axeplyr Supporting Member

    Messages:
    1,701
    Joined:
    Mar 26, 2004
    Location:
    Nelson Bay, Australia
    I'm getting ready to get into amp building. I've spent considerable time reading up on the subject, and I'm getting ready to build something resembling a 5F1/5F2A Champ/Princeton. It's easy enough to identify a whole bunch of compatible PT's and OT's that will do the job. However, I am leaning forward to my next project - a 5E3 type - and realized I can probably buy these transformers carefully and slightly overspec'd, thus preventing me from having to rebuy when I decide to tweak/redesign for potentially push-pull or SE EL-34/6L6 designs.

    So, I've narrowed down a couple of potential transformers:

    PT: 370EX
    OT: 125ESE

    I picked these because they seem to be usable for a variety of circuits. However, I get conflicting info on the 125ESE; it's optimized for single-ended class A, yet some seem to indicate they've used them for class A/B push-pull.

    These are the types of things I'm concerned about. I'd really like to be able to buy a single set of transformers and get alot of flexibility. Anyone tried this? Are there better transformers for what I'm trying to do, and can handle everything from SE 6V6/EL84 to push-pull 6V6/EL84 and up to a single tube SE 6L6/EL34/KT66 design? Or should I resign myself to buying multiple transformers?

    Thanks!
     
  2. SatelliteAmps

    SatelliteAmps Member

    Messages:
    6,185
    Joined:
    Oct 19, 2007
    Location:
    Normal Heights, Calif
    They won't work as a universal set. They will work for a champ project. An output transformer that will be good for a single 6V6 (i.e. Champ) will not be great for a pair or EL34s (Push-Pull). The PT will work for the 6V6, but it will not work to run even a pair of EL34s. The PT does not provide enough amperage. A single EL34 needs 1.5a, and that transformer only puts out 2.5a.

    There are some great universal transformers out there, including some vintage Triade's. I would recommend getting purpose built transformers for your Champ project (i.e. specific for a Champ), and then start looking at what you NEED in a universal PT and OT.
     
  3. Axeplyr

    Axeplyr Supporting Member

    Messages:
    1,701
    Joined:
    Mar 26, 2004
    Location:
    Nelson Bay, Australia
    I had only planned a single EL-34 or 6L6. The push-pull would be for a pair of EL-84's or 6V6's.

    Both the PT and OT I chose are significantly overspec'd to the Champ circuit and the Tweed Deluxe circuit. I spent considerable time looking for transformers that people used in a variety of different projects.

    The 370EX PT is has 275-0-275/125mA, 5v/3A and 6.3v/4A secondaries, which according to my research should handle a single EL-34. In addition, it should work fine with a single 6L6, two 6V6's, two EL-84's, a single 6V6, or single EL-34.

    the Hammond 125ESE is being used in amp projects utilizing a single EL-34, 6L6, or a KT66 in an single-ended config.

    So I've accounted for the overspec. My questions are:

    1. Will these transformers sound good in a Champ/Princeton circuit?

    2. Will the 125ESE transformer (designed for single-ended operation) sound OK in a push-pull dual 6V6 or dual EL-84 circuit?

    Part of the problem is I live in Australia, where these transformers aren't $50 each! They're $150 to $300 each. So I'd like to buy a single set and have max tweakability!

    Thanks,

    John
     
    Last edited: Mar 5, 2011
  4. SatelliteAmps

    SatelliteAmps Member

    Messages:
    6,185
    Joined:
    Oct 19, 2007
    Location:
    Normal Heights, Calif
    Sorry, my mistake. I read EL34 when you wrote EL84. Hammond transformers sound decent, so they should sound OK, but probably not exactly like a Champ/Princeton. They will also sound OK in a dual 6V6/EL84.
     
  5. rooster

    rooster Member

    Messages:
    2,123
    Joined:
    Mar 9, 2005
    Location:
    Arizona
    IIRC, the 125E is the one that can be used for push/pull and single-ended. The 125ESE is a single-ended only air-gapped OT. I think. I could be wrong, though, it's what I do best.

    rooster.
     
  6. Axeplyr

    Axeplyr Supporting Member

    Messages:
    1,701
    Joined:
    Mar 26, 2004
    Location:
    Nelson Bay, Australia


    Thanks. More more I read, the more I realize I need to learn. Apparently the 125ESE is not physically suited for a push-pull amp because it lacks a center tap. The 125E will apparently wor in a pinch but is not optimal. I might just have to reconsider all of this and go with a dedicated Champ or Princeton set as per Satellite's original suggestion.
     

Share This Page