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My Twin conversion: quest for TONE!!

Discussion in 'Amps and Cabs' started by creamedcorn, Feb 19, 2009.

  1. creamedcorn

    creamedcorn Member

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    Jan 15, 2007
    Location:
    Beantown
    Fellow gear nuts,

    Finally my Twin Reverb conversion is here! This is the '71 Silverface Twin (non-master volume) that I bought new (for the Floridians: at Ace Music on 7th Ave.). $400, which I payed off by working with my Dad for a couple of years of Saturdays (2AM to 3PM). I played the crap out of this amp up until the early 90's, when I closeted it, because it was too loud for the venues I was playing. About a year ago, I hauled it out for a studio gig, and sadly, it died from neglect.

    Enter Rob Lohr - amp wizard, currently tech for Aerosmith, and working a bench at a small Mom and Pop music store in Allston (Mr. Music). I had him rebuild my baby to '66 Blackface specs, plus a master volume . Because I'm too old and decrepit to lift the twin, I turned it into a head, and did it in blackface cosmetics.

    This sounds AMAZING! It is super "HI FI"! Classic reverb, and trem.

    There's still more to go - we used the original pre-amp tubes (!). As cash allows, they'll be replaced with EH's. And eventually, Mercury Magnetics transformers, with taps for different speaker options. Speakers!!! ????????????????

    Before:

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    After:

    [​IMG]

    [​IMG]

    [​IMG]
     
  2. Tread

    Tread Member

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    2,008
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    Location:
    Viginia
    Thats really kool man!.
    I'm working on an old twin right now.
    Very Kool!
     
  3. Steven_K

    Steven_K Member

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    Location:
    Chicago, IL
    Why would you swap out the original transformers? I know its a bit of a pain to only have one impedance option, but the whole reason mercury magnetics exists is to build copies of what you already have.
     
  4. b2sc

    b2sc Member

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    This is the first time I've ever heard of someone installing a master volume in a NMV TR. Ouch. And you plan in replacing the orig. transformers? Don't forget to replace the PTP board w/a surface mount PCB after that.

    Who are you, Benjamin Button? :)
     
  5. DC1

    DC1 Member

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    The MM Axiom series are supposed to be an upgrade from the original. It is the Tone-Clone that are designed to sound like the originals.


    BTW, be careful with changing preamp tubes. Only change one at a time and then listen. You may find you original preamp tubes to be just fine and better than the new-production ones.


    dc
     
  6. creamedcorn

    creamedcorn Member

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    Location:
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    I'm not a tech - and I'm not a purist - but this MV is not wired as usual (I'll ask Rob for details.). Frankly, I don't like so far, and if I don't find a use for it, I'll pull it out.

    Apart from the MM Axiom impedance options, as I understand it, they boost the voltage. But the bottom line for me is that the A/B clips I've heard sound significantly better. True, the MM Tone Clones are reissues, but since my amp was rebuilt to BF specs, the BF MM TC trans should sound better.

    I'm just happy to have the amp working again. The stock '71 sounded good to me - but I was 14 years old when I bought it. What did I know about amps? What I did know then, it was F--king LOUD! 38 years later, I know what I want to sound like, and this is getting close.
     
    Last edited: Feb 20, 2009
  7. Squigglefunk

    Squigglefunk Senior Member

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    congrats on a great looking refurb on that beauty, rock out!
     
  8. creamedcorn

    creamedcorn Member

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    Location:
    Beantown
    For the tech minded, here's Rob Lohr's regarding the master volume circuit on my twin:

    "Look at the 1st schematic I've attached (AB763 twin rev.). Towards the right hand side of the page you'll see the 6L6 output tubes each with a 1.5k resistor at it's input. Supplying the bias to the outputs are two 220k resistors. Just to the left of the 220k resistors are two .1uf capacitors that supply the signal from the phase inverter to the outputs. The master volume circuit goes here, in between the .1uf caps and the bias resistors. it consists of a dual concentric 1M audio taper potentiometer and a second pair of .1uf capacitors. The signal from both existing .1uf's is connected to the top of each of the two sections of the dual 1M pot. the bottom of both sections of the pot are tied together and connected to chassis ground, and the wipers of both pots (the outputs) feed the two "new" .1uf caps which now feed the outputs at the points where the 220k resistors connect. The typical place for a fender master volume is just before the .001 cap which is the input to the phase inverter (like in a marshal). This design is like more modern Fender custom shop amps (see second attached schematics- tonemaster). You'll note the tonemaster also utilizes a relay that functions as a foot switcheable master volume bypass... the point of doing the master volume this way is to have less of an effect on the tone/overdrive characteristics of the amp when the master volume is turned down. It will always have SOME effect, but far less than the typical circuit, especially when used sparingly. That being said, if you find yourself wanting to turn the master down "too much", you can bring the amp in and have me pull two outputs and re-bias it for 45 or 50 watts. Or, I'll be happy to take out the fancy stuff and make a regular silver face twin style master if you prefer. I can perform either opperation in 15-20 min. while you wait! :)"

    [​IMG]

    [​IMG]

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  9. RedRock

    RedRock Member

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    This kind of post phase inverter master volume (minus the relay) was used about
    20 years ago by Marshall in their Club and Country combo, and also
    discussed as one of 4 possible master volume controls by the late great
    Ken Fischer in "The Trainwreck Pages," about 15 years ago.

    It does work well by allowing the phase inverter tube to distort before
    controlling amp volume. The 2nd set of caps prevent the bias voltage
    from being grounded by the dual pot.
     
  10. joolzriff

    joolzriff Member

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    dude! i died laughing
     

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