Build: 10 Watt Vibro Champ 1x12 Combo

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

  1. FenderLover

    FenderLover Poster Extraordinaire

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    You mentioned EL34 earlier, it may drive a little better at higher voltage.
    Ultimately, your 40-18109 only has 100mA to offer. You are squeezing it for the last bit of juice. I'd say keep squeezing!
     
  2. tubelectron

    tubelectron Tele-Afflicted

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    It's a nice build, a neat work - congratulations Phrygian77 ! :cool:

    IMHO, expecting 10W RMS output clean tone on rated impedance with a single EL34, 6L6 or the like with only 334VDC plate to cathode is optimistic. o_O I'd rather say that you would be around 6-7 watts clean tone (@400Hz, sine wave, just under the clipping onset on the scope).

    It's what I notice on my similar builds (SE 6L6/EL34). My power transformer is a 300V/0.1A HV secondary, plus solid-state rectifier and 100µ/500V filter caps + choke. Sorry I don't have my schematic on hands to confirm the exact matching DC voltage values, nor the plate load I used (Hammond 125BSE transformer). I tested an EL34 and a 6L6 with no significative power output difference.

    Like you planned to do it initially, I used a 8" speaker... Perfect for home use, but not for gigging, you said it... ;)

    [​IMG]

    On his mate, fitted with a 8" too, I integrated the tremolo effect of the Vibro-Champ, and and I agree : it's a good sounding tremolo...;)

    [​IMG]

    [​IMG]

    [​IMG]

    It's a SE 6V6GTA output stage, where :

    Vp = 314V
    Vs = 310V
    Vk = 19.6V
    Rk = 470R/5W + 22µF//

    For a mighty 3WRMS clean tone output, via a (too tiny) 1750A Hammond transformer (5K/8R).

    [​IMG]

    But it's me, OK ? :D

    -tbln
     
  3. Phrygian77

    Phrygian77 Friend of Leo's

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    IMG_20190802_140201.jpg

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    I did some side by side testing with my blackface Bassman combo setup the way I usually gig with it, and I think this thing might just be loud enough. I'll find out tonight! It's also not as warm as I thought either. The stronger bottom end of the Bassman though with those 6L6s and the bigger cabinet was very apparent. It seems a little louder in the combo cab with the GB128 than it was through my Weber 1225 loaded 1936 cabinet.

    I could turn this build into a head, and pair it with a 2x12 cab, maybe with a GB128 and a 1258. I still have another Vibro Champ chassis and a lot of faceplates! I may try to build the AA964 non-reverb Princeton circuit into one with JJ 6V6s SS rectified.



    Yeah, lowering the NFB level would certainly increase the volume some. I would think that would make it a bit more midrangy also. I've got an NFB switch on my Bassman (it's way too loud and dynamic that way), and I put one on one of my PR builds.



    I've got a 12" Scorpion (did I mention that in a previous post?). I like it OK. It reminds me of an EV or an Altec, fairly flat and uncolored.



    I did that with the 5F1 circuit that I built in a PR chassis and cabinet. A 1uF works really well with the 1.5k cathode resistor. If I up the mid resistor, or add a mid boost pot (which I may do), I'd probably do that to tighten up the low end some.



    That's why I bought the M6 version. I thought the 40-18027 that I've used in my PR builds might run a little hot, especially using the 550 secondary with an EL34.



    Thanks! I haven't scoped it yet, but I think it's right at about 7 watts.
     
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  4. Phrygian77

    Phrygian77 Friend of Leo's

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    Can you gig with it? Yes! Yes, you can! It really surprised me how well it did with our 5 piece group in the little restaurant tonight. So, here's your blueprint for a single-ended giggable amp. Any less sensitivity in the speaker and it probably wouldn't have worked out.

    MVIMG_20190802_204121 (1).jpg
     
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