Bassman Output Transformer Replacement questions

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers T' started by tapeup, May 4, 2012.

  1. tapeup

    tapeup Butterscotch Supt. Member Gold Supporting Member

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    Hello, I've searched for this, and haven't quite found the information I'm looking for yet. Maybe some people here can help.

    I have a '66 Bassman head that was acting up, and upon taking it to a tech, I found out it had a replacement output transformer in it that was not the correct replacement for this amp, which was causing the amp to run improperly, and needs to be replaced.

    My question is, which company and which model transformer is ideal? I've read lots of back and forth debate over whether or not it's worth it to spend extra money on Mercury Magnetics transformers, and I don't know what to believe. Can anybody steer me in the right direction so I can get this amp back in playing condition again?

    Thanks for any and all help, I appreciate it! Cheers!
     
  2. wyatt

    wyatt Member

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    Normally, I would go for an Allen, but they don't make offer anything above 40 watts. So I recommend ClassicTone...they offer a straight Bassman Head replacement...model 40-18011. Otherwise, Mojotone.

    Mercury makes a great product, but you get nothing extra for the extra cost versus ClassicTone, Allen, Mojo, etc.
     
  3. Hwoltage

    Hwoltage Member

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    You should also engage your tech in this conversation. All the different transformer makers vary a few things here and there, but aside from having a transformer with enough sheer bulk (iron dimensions) to support the low end without crapping out, the most important thing is to have the correct impedance ratio for the amp's particular speaker load, tube configuration, and *desired* bias setting.

    If your tech knows why the transformer is "wrong" he should know what is "right" and will be capable of steering you in the right direction.
     
  4. 3th3r

    3th3r Supporting Member

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    The Mojotone 774 OT is made by Heyboer, which IMO are a great value -- great sound at a reasonable price.
     
  5. gldtp99

    gldtp99 Member

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    I'd use the Classic Tone upgrade BF Bassman-type OT: http://www.classictone.net/40-18001.html
    I've used this OT in many builds and replacements---a superior sounding OT at a great price--- my own BF Bassman runs one of these--- 4/8/16 ohm output taps make running almost any speaker cab a breeze..............gldtp99
     
  6. zzmoore

    zzmoore Supporting Member

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    I am just curious.
    Almost nothing in a tube guitar amp follows spec.
    What OT is/was in your amp that was causing these problems.? Or was it more than just the OT.?
    Best
     
  7. guiltless

    guiltless Supporting Member

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    +100

    Using this one as well. Sounds great!!!
     
  8. tapeup

    tapeup Butterscotch Supt. Member Gold Supporting Member

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    Thanks for all of the replies so far guys. I appreciate the help!


    I don't have the notepad in front of me from where I wrote down all the information from the conversation I had with the tech, but from what I remember, the transformer that was in the amp was a tweed bassman replacement, and it was causing the plate voltage to be way too high. Does this sound like a possibility?
     
  9. Hwoltage

    Hwoltage Member

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    You need to know thew exact make and model of the transformer that is in your amp. From that you will be able to find the impedance specifics and determine if it is in fact the wrong transformer.l

    Does the secondary have multiple taps (4, 8 16 ohm etc)? If so make sure the correct tap is being used for the particular speaker load you are using.

    Assuming both Bassman versions are two tube 6L6 push pull-amps the transformers *shouldn't* differ much. For example, the Hammond Tweed replacement has an impedance of 4200, the '59 has 4150 and the "Bassman" is 4000.

    http://www.hammondmfg.com/guitarLineOT.htm

    This impedance coupled with the speaker load is what reduces the voltage (although very slightly) through the transformer, which is why I say to check that the proper tap is being used as this will either lower or raise the impedance from the proper specs.
     
  10. walterw

    walterw Gold Supporting Member

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    not an amp tech here, but wouldn't the "tweed" version want to see a 2Ω speaker load?

    maybe that's the problem.

    anyway, +1 to classictone trannys; i had the Magnetic Components blackface bassman OT installed in my early '70s pro reverb (the straight-up 4Ω one, not the one with multiple taps) and it turned that amp into a monster.
     
  11. tapeup

    tapeup Butterscotch Supt. Member Gold Supporting Member

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    I have a slight update to the situation, but an important piece of information nonetheless.

    It is the power transformer that had been replaced with an improper unit at some point, not the output transformer.
     
  12. Chris Scott

    Chris Scott Member

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    Mojo 762

    ...about $69. last time I checked. It's a Heyboer as well...
     
  13. tapeup

    tapeup Butterscotch Supt. Member Gold Supporting Member

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    Okay awesome, thanks for the quick reply Chris! I appreciate the help!

    I see you're in Jaco, how's the surf been lately? I haven't been to Costa Rica in way too long! :cry:
     

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