Build: 10 Watt Vibro Champ 1x12 Combo

Discussion in 'Shock Brother's DIY Amps' started by Phrygian77, Jul 26, 2019.

  1. Phrygian77

    Phrygian77 Tele-Afflicted

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    I was expecting a 1x8 cabinet, but this arrived instead...

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    So, I'm going to roll with it. I was originally planning to do a standard Vibro Champ first, then do a 10 watt version as a head.

    I'll be using the 15 watt ClassicTone 40-18031 OT, using the 5k primary for a 5881 or EL34. PT is the ClassicTone 40-18109, using the 550VAC secondary SS rectified.

    Checking fitment of components here...

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    I'm wondering if the closeness of the OT to the cap can is going to be a problem. These are 32+32 cans that I had for my Marshall build. I was going to do 64 for the main filter, 32 for the screens, and 32 for the preamp. Cathode bypass cap for the power tube will be a 100/100.
     

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    Last edited: Jul 27, 2019
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  2. Jorgen83

    Jorgen83 TDPRI Member

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    What speaker are you using?
     
  3. Phrygian77

    Phrygian77 Tele-Afflicted

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    Well, I don't know yet. I haven't decided. I didn't plan for this, so I've got a WGS G8C sitting in an unopened box. I've got an old Altec and a Scorpion laying around, but I'm not going to use those.
     
  4. lowatter

    lowatter Tele-Meister

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    Nice mishap in your favor. Looks like it's intended for a Fender Musicmaster Bass amp instead. An EL84 build will be great in that cabinet. As far as a 12" speaker for it I would recommend a Celestion G12H if you can afford it or maybe just any 12" Eminence for Fender from a Blues Jr would be just fine and are cheap on evil bay because a lot of Blues Jr owners replace those for upgraded ones. I'll be watching this thread and looks like you're off to a great start.
     
  5. Phrygian77

    Phrygian77 Tele-Afflicted

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    No, it had a sticker on the side of the box that said Vibro Champ 1x12.
     
  6. Rich_S

    Rich_S Friend of Leo's Gold Supporter

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    I have a MuchSX Champ built into a head, paired with a LopoLine open-back 1-12" cabinet. I put an Eminence 1258 in there. It's just a plain-jane, non-booteeky, American-voiced 12" but it sounds great, is louder than hell, and was cheap.

    Even with a normal 5-watt Champ, our keyboard player once asked if we could move it to the other side of the stage because it was too loud, and it wasn't even pointed at him.
     
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  7. schmee

    schmee Poster Extraordinaire

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    "I'm wondering if the closeness of the PT to the cap can is going to be a problem. These are 32+32 cans that I had for my Marshall build. I was going to do 64 for the main filter, 32 for the screens, and 32 for the preamp. Cathode bypass cap for the power tube will be a 100/100." if you meant the OT, just diagonal it.
     
  8. FenderLover

    FenderLover Friend of Leo's

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    Cool build. I think you'll be leaving a few watts on the table if you want to bias up a 6L6GC with the 550V winding. If you use the 660V winding, you'll match the 5K OT real well. A few watts won't matter much to output volume, but will fit your OT better with the higher B+.
     
  9. lowatter

    lowatter Tele-Meister

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    I suppose, however the cabinet looks like it could house a Musicmaster Bass nicely.
    [​IMG]
     
  10. printer2

    printer2 Poster Extraordinaire

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    The cap might be a touch warmer than if the transformer was farther away. I would drill a couple of holes and mount the OT a little farther but it might not matter too much.
     
  11. Phrygian77

    Phrygian77 Tele-Afflicted

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    I didn't realize they're the same size chassis.

    It has to go there, or I'd have to ditch the fiberboard that I have, and elevate a Garolite board on standoffs... And, that's not happening.
     
  12. printer2

    printer2 Poster Extraordinaire

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    Then there is no question, it will be fine.
     
  13. Phrygian77

    Phrygian77 Tele-Afflicted

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    A lot of progress so far. I should have taken more pictures, but I was too busy working.

    Pilot holes drilled in the eyelet boards for the mounting screws. Here I've just got the insulator board taped down to chassis to use as a template. Holes were all drilled with the drill press...

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    Test mounting the board. These are 5/16" 8-32 Swageform screws (thread forming). Holes were drilled 9/64.

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    I've built a blackface Bassman, and three Princeton Reverbs with chassis from Zachmdhunter, and this is the first time I've had this problem. Same Belton 9-pin sockets that I always buy from Hoffman...

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    I didn't expect that, so I thought I was done drilling and filing. I had already wiped down the chassis with mineral spirits. :( A little elbow grease with a small round file, and wiped down again...

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  14. Phrygian77

    Phrygian77 Tele-Afflicted

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    For some reason, the Mojotone fiberboard didn't have the holes drilled for the V1 grid wires that go under the board (the ones that come up over the 100k slope resistor). You can see in my last post where that I drilled them myself. This is why I normally like to make my own boards. I was just trying to save time.

    It's not the first time I've had an odd problem with a Mojotone board. The blackface Bassman board didn't have the through hole for the second channel tone control wires. Also, the large blackface style filter board that I got was upside down, i.e., the eyelets were installed on the wrong side. @JKube had the same problem with the Mojotone cap board on his Twin Reverb build.

    Moving on, I probably should have put more thought into the layout. We'll see how this works out. I'm going to have to tuck a lot of extra transformer wires somewhere also...

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    Last edited: Jul 29, 2019
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  15. Phrygian77

    Phrygian77 Tele-Afflicted

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    I thought this was going to be a really easy build, at least compared to the Princeton Reverbs builds. Well, not so much.

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    I'm not sure about my lead dress on the oscillator and cathode follower, but I don't know that it really matters that much. The lead dress examples I've seen in pre-CBS Vibro Champs didn't look so great. In this case the board is offset some because of the Keps nuts, so I couldn't really copy what Fender did anyway. I've got custom stuff everywhere, e.g., multiple can caps, variable cathode bias. I'm winging it.

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  16. Phrygian77

    Phrygian77 Tele-Afflicted

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    Ugh... thought I'd be done by now now.! Ready to fire it up! Maybe tomorrow night. :(

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  17. Phrygian77

    Phrygian77 Tele-Afflicted

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    Well, I'm a little disappointed. The clean tone isn't quite what I expected considering that I used a 6.8k mid resistor instead of a 15k. It seems a little dull, lacking some top end. The plate voltage was lower than I was anticipating, 334VDC plate to cathode. Maybe that's why it sounds a bit warm? It could also just be my ears today. I still need to A/B it with another amp.

    Right now, it doesn't sound quite loud enough to gig with. I'm tempted to try the 630 secondary, but think that would be a bit too much for the 5881.


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    I do like the tremolo a lot. Just as good as my PR builds, and definitely better than the opto coupler type.
     
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  18. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Maybe raise the NFB resistor a bit to add some brightness and volume. The Princeton Reverb I built this year really benefitted in both areas with a double value NFB off the speaker jack. Left the tail the same. After I got used to it, the stock position just sounded like it had a blanket over it.

    Sent from my XT1585 using Tapatalk
     
  19. JeffBlue

    JeffBlue Tele-Afflicted

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    Your project is certainly a good one. I have a 1968 Silverface Fender Vibro Champ that I modified with a Mercury Magnetics output transformer (57 tweed) and modified the cab for a 10 inch speaker. I installed a 10 inch 4 ohm Peavey Scorpion and this amp sounds incredible. Don't overlook the Scorpion.
     
  20. Intubator

    Intubator Tele-Meister

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    Try lowering the v1 bypass cap value to bring up the mid and treble. Last year i built a Champ in a tweed Princeton cab with a 12" 15w Weber and I ended up changing that cap from 22uf to 1uf. That change really woke the amp up and it sounds fantastic, like it was built to drive a 12". I had experimented with a bunch of values too, but to my ears the 1uf was the best.
     
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