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Vibro Champ Build

Discussion in 'Shock Brother's DIY Amps' started by brucerbc, Dec 5, 2020.

  1. brucerbc

    brucerbc TDPRI Member

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    Starting the Vibro Champ build that I'd asked some questions about in an earlier thread.

    Board populated and leads mounted:

    20201202_225857[1].jpg
    A little sloppy with the flux, but it really helped the solder take to the eyelets:

    20201202_225908[1].jpg

    Most chassis-mounted components in place too:

    20201202_225930[1].jpg

    Hope to get the transformers mounted and off-board wiring completed this weekend.

    20201202_225943[1].jpg

    Only frustration so far is that the cap can hole is too small to mount my CEM multi-cap using a clamp, so I'll solder that.

    Well, I also scratched the faceplate while mounting the power switch ... but touched up with felt pen.

    Any questions, observations or constructive criticism is welcome!
     
  2. daveIT

    daveIT Tele-Holic

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    Awesome! Looking forward to the completed amp!
     
  3. BigDaddy23

    BigDaddy23 Tele-Holic

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    Looks good mate. The only thing I would suggest is to not twist the power tube cathode bias resisitor leads around the cap leads. You may have to change that resistor value once you fire it up and take bias measurements.
     
  4. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Along this line, I'm not sure why people attach the electrolytic cap to the eyelets/turrets and then piggyback the cathode resistor off that. The cap is what's going to need replacing first, not the resistor. ;)

    But I am interested in watching this build take shape!
     
  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Drill a hole for the power cord ground bolt near the power transformer side of the chassis before you get too far.

    Speaking of ground, what ground scheme have you chosen?
     
  6. radiocaster

    radiocaster Poster Extraordinaire

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    Cathode bias is pretty forgiving, unless you're going for something special like super hot bias.

    And despite what I wrote, I could be wrong and am interested in your take on this.
     
  7. BigDaddy23

    BigDaddy23 Tele-Holic

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    Whilst that is true that cathode bias is forgiving, the voltage coming out of your socket may be higher/lower than intended. You want to be able to set the bias where the amp performs best sonically. It may well be that the resistor value in place is fine but if you do have to look at a different value, it is far easier to change if it goes straight into the eyelet.
     
  8. mojek

    mojek Tele-Meister

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    Very nice build and respect, it needs a patience! Solder joints look fine, much better than some original out of the factory ones:)Curious about the result;)
     
  9. radiocaster

    radiocaster Poster Extraordinaire

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    "Sounds better" generally means "hotter bias". The tubes may wear out faster if it's a very hot bias, and you may have less choices of what brands you can put in for that reason.
     
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  10. Linkjr

    Linkjr Tele-Meister

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    I used isopropyl alcohol to clean the flux works a treat, On my build and imho I didn't notice that much of a change with the NFb on off mod but got wild and wicked with a tone stack bypass mod. You might find like me it is already a pretty gainy amp.
     
  11. brucerbc

    brucerbc TDPRI Member

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    Almost done, but not quite.

    Front[1].jpg Back[1].jpg Top[1].jpg

    Only the power cord left to wire, but I had wrong size of strain relief on hand for this chassis and don't want to drill out the punched 1/2", no rotate mounting hole.

    Now waiting for that part (along with components for next build).

    Hoping here and done in a couple of weeks, but holiday shipping may delay.
     
    2L man likes this.
  12. brucerbc

    brucerbc TDPRI Member

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    Posting progress, but good news and bad.

    I have sound, volume control and tone control, but no tremolo and many voltages off from Fender layout.

    Likely connected, I know, but will need some help troubleshooting from this kind forum.

    Will post pictures and voltages here for now, but ... please point me to a list of measurements to provide if I've missed anything?

    All voltages relative to ground.

    Fuse: 122.1 VAC

    Switch: 122.1 VAC

    V1 (12Ax7)
    pin 1 - 249.9 VDC (steady)
    pin 3 - 2.04 VDC (steady)
    pin 6 - 252.0 VDC (steady)
    pin 8 - 2.03 VDC (steady)
    V2 (12Ax7)
    pin 1 - 150-235 VDC (fluctuating)
    pin 3 - 1.70-1.72 VDC (fluctuating)
    pin 6 - 405 VDC (steady)
    pin 8 - 193-204 VDC (fluctuating)​

    V3 (6V6)
    pin 3 - 400 VDC (steady)
    pin 4 - 407 VDC (steady)
    pin 8 - 32.2 VDC (steady)​

    V4 (5Y3)
    pin 2 - 412 VDC (steady)
    pin 4 - 350.2 VAC (steady)
    pin 6 - 350.2 VAC (steady)
    pin 8 - 412 VDC (steady)​

    Cap Can
    380 VDC (steady)
    408 VDC (steady)
    413 VDC (steady)​

    OT: Hammond 1760C
    PT: Hammond 290AX

    And please let me know if I should post in a separate tech help thread?

    Thanks!

    Vibro Champ - Layout - Fender.gif

    Top.jpg

    Top - Pre.jpg

    Top - Power.jpg

    Inside - Front.jpg

    Inside - Back.jpg
     
  13. brucerbc

    brucerbc TDPRI Member

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    So, I've spent a bunch more time checking parts, wires and voltages.

    Other than observing voltages consistently higher than Fender layout across the amp (as posted above) ... and not hearing and tremolo (sounds same as dry) ... I'm finding nothing.

    Everything else looks right ... (famous last words).

    Would higher than spec voltages be enough for the tremolo to not work in a Vibro Champ?

    Or are the voltages close enough (+20%?) that I should move to biasing?

    Any advice appreciated.

    Also would be super helpful if anyone can point me to "bias measurement and calculation for dummies" or similar. Especially if on the dumber end of things.
     
  14. Boreas

    Boreas Friend of Leo's Silver Supporter

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    Forgive my ignorance, but is this a kit? If not, where did you come up with the chassis and faceplate? Color me interested.
     
  15. brucerbc

    brucerbc TDPRI Member

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    Not a kit. Chassis, faceplate and eyelet board from SolandFa. Other parts from various suppliers. Built following Fender layout.

    Any troubleshooting tips?
     
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  16. Boreas

    Boreas Friend of Leo's Silver Supporter

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    Unfortunately, no. But I appreciate the information. I am looking forward to you getting it sorted and finished. I would like to build one myself, but don't know if I have the chops.
     
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