Bassman micro in an 18W Marshall chassis - power transformer mounting?

Discussion in 'Shock Brother's DIY Amps' started by Dbsoundman, May 16, 2021.

  1. Dbsoundman

    Dbsoundman TDPRI Member

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    Hi all, I'm hoping to use the pre-drilled Marshall 18W chassis from Mojotone for my Bassman Micro build, but I'm a little confused on how to mount the power transformer. Rob specifies a stand up Hammond power transformer, but the chassis has a cutout for a laydown style transformer. I found the Hammond 290AAX on this page, which is made to replace the transformer in the Fender Musicmaster Bass amp and provides basically the same voltages as the transformer Rob found, however I think it's actually a little bit too small for the hole in the Marshall chassis.

    Should I just get the Mojotone chassis and cut my own blank to cover the transformer hole? I'll obviously have to get some tube socket blanks anyway. Just curious if anyone else out there ran into this and came across a better solution. I'd really rather not drill my own chassis when the 18W provides pretty much everything else I would need already.
     
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  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Ime, that's a good plan. You might look into the toroidal PT to cut cost and possibly reduce noise. It is lighter too.
     
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  3. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Mounting a different PT would probably be worth whatever pain it would be... the front panel will have the correct holes and labels.

    I’ve used sheet metal scraps and bolted them over the cutout.

    If the chassis is big enough and the PT small enough, you might be able to just leave the cutout and scoot the PT next to it. Though, 18watt chassis aren’t usually big, nor are their PTs.
     
  4. Dbsoundman

    Dbsoundman TDPRI Member

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    Well, the Mojotone 18W chassis arrived today, and I realized that I mis-measured the cheap Marshall combo cabinet I picked up at the LGS. Chassis is 17"+, the inside dimension of my combo cab is about 16". Grr.

    At this point, I really want to stick with the 18W chassis, so I think I'll just build the amp in that chassis and mount it to a piece of wood temporarily, then eventually I'll either get a JTM45 head cabinet, or build some other kind of enclosure. I'll just fill the blank space in the Marshall cab with a piece of wood and call it a day. I just really, really don't want to custom drill my own chassis, then have to try to match up a faceplate.

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