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Conn Organ Amp Conversion to Tweed Bassman

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  • Conn Organ Amp Conversion to Tweed Bassman

    Conn organ amp is up and running.

    I do these once in a while but I don't take much time to explain the process.

    Obtain amp...free is good.
    But you really don't want to pay much due to the fact that many organ amps, PA amps, and "other" tube amps may not have much that is usable for a guitar or bass amp.

    First thing I try to do is get that amp-as is, up and running so I know what I have.
    Sounds simple but it can really challenge the troubleshooting skills plus organ amps have so many other functions going on...it has to be divided up and conquered.
    PA amps can also have everything including the kitchen sink thrown in, as if they are integrated mixing units with multiple impedance inputs and outputs designed to drive other power amps.

    So I examined the Conn, determined it was safe to bring up with the variac while watching current draw (I really need to build a light bulb limiter...) which reforms the old canister caps.
    M-fugg, this thing is LOUD for being a simple 2x6L6...but sounds good, no hum.

    So now comes the hard part-is it close enough to convert?
    Does it need to be gutted and rebuilt?
    Or is it just good on its own?

    Well time to sketch out what is in it, and research the brain and schems for
    what fits.
    I'll be gummed, looks REAL familiar.

    Tweed bassman, but with a single 12AX7A instead of 12AY7's.
    And cascaded already!
    Cool, let's try it.

    So I dig further into Leo's brain and I find a good fit-the Princeton followed a similar path.

    So I installed jacks, volume and Princeton 5D2 style tone stack.
    Sounds nice...and LOUD!

    Turns out the only conversion is adding a few components to make it guitar-friendly
    and cleaning up the stuff that I didn't need in there.





    I see a problem with making a head cab though.
    The power transformer is directly up against the chassis face.
    No room for the cover!

    Similar problem with placing the controls, too close to the output transformer so I had to squeeze
    it all on one side.
    The voicing is close enough to not have to mod the whole amp - a big plus.
    Has a couple of blue molded caps in it...good stuff.



    Also found out I have some Mullard 12AX7 pulls!
    Along with a Mullard 5AR4/GZ34.
    Cork sniffer tubes...I'll have to give those a try in the Cyg combo.

  • #2
    pretty awesome!! could you make a new chasis?
    GEAR:

    some guitars...WITH STRINGS!!!! most of them have those sticks like on guitar hero....AWESOME!!!!

    some amps...they have some glowing bottle like things in them...i think my amps do that modelling thing....COOL, huh?!?!?!

    and finally....

    i have those little plastic "chips" used to hit the strings...WHOA!!!!

    Comment


    • #3
      You use your tongue prettir than a... oops.. Sorry. Sounds great for being greek!!

      Hammond M3 organ amp came up on CL for $50. Thought about asking you if I should buy it but realized that I still have no idea WTF I'd be doing with it.. Your post just proved me right!!
      Every man dies... Not every man really lives!!

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      • #4
        Originally posted by markD View Post
        pretty awesome!! could you make a new chasis?
        Thank you warlok (I think...).
        Conversions are a good way to learn if you are committed to giving it a try.

        markD-I'll try to reuse the old chassis if I can but sometimes have to go with a new one.
        Swiss cheese isn't always good.

        Comment


        • #5
          Looks like they cut the bottom off a coathanger to use as a bus line there hehe... Not exactly milspec point to point wiring but I guess as long as there isn't shorts, it's all good.
          GTWGITS! - RacerX

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          • #6
            SOUND CLIP:

            I don't allow my lack of talent
            to stop me from trying to display what a good amp sounds like...

            Noodling (of course) I'm trying to display the characteristics of this amp.
            Imagine a 50 watt Princeton.
            The amp is barely cracked open, and it still overloads the SM57 clone (Samson) at 2 feet away, and I'm generally picking softly.

            There's a couple times you start to hear that "bloom"...it achieves it nicely.
            Guitar is a Jackson DKMGT with a J90C bridge and a neck pup from a Dinky Concept.
            No mid-boost or overdrive.
            Cab is the 5150 Block, which I now realize has an issue...(rattles).

            The cops aren't here, so all is good.

            Enjoy...

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            • #7
              Got a wild hair and tried a Fischer master volume style #1 on it.

              I'll be gummed, it works quite well!
              As with nearly every MV mod, it's wise not to over do it.
              Running it up halfway seems to do the trick.
              Made a noodling soundclip with a Fuaux-LP fitted with a set of Dave Stephens pickups.
              Vintage Lab 3 prototype and an unobtanium PF Star prototpye in neck and bridge.
              (VL3 in the bridge).
              Home: SD Pickups, Custom-Made Hand Wound Guitar Pickups by Dave Stephens, Stephens Design


              Forgive the background noise, the guitar is not properly shielded.
              The amp is not dialed up much at all.
              Channel vol 50%, MV just cracked.
              2x12 Weber alnico sigs (Yeah, I know...) in a 67 Bassman cab.
              Guitars tone and vols set at about 75% leaving plenty of headroom, I left them there for the duration of of the clip.

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