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Questions on variations of the blackvibe circuit

Discussion in 'Shock Brother's DIY Amps' started by zorgzorg2, Sep 19, 2020.

  1. zorgzorg2

    zorgzorg2 Tele-Meister

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    One more question that came to me: which ground should I use for the master volume's AC caps to connect to? Same as the b/c/d filters?
     
  2. zorgzorg2

    zorgzorg2 Tele-Meister

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    OK, so for the transformers, I'm going to use:
    Hammond 290D2EX for power
    Hammond 194B for choke
    Hammond 1760J for output

    The E in 290D2EX means export so that it support up to 240V as input.

    As a speaker, I chose the WGS G12C/S. It's going to be in a separate cabinet.

    I had to order the parts from four different providers to get everything, but now I'm just waiting for the parcels to arrive. Can't wait!

    I already have a board and eyelets, so I'll be starting with that over the week end.
     
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  3. EmWeAh

    EmWeAh Tele-Meister

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    As a PT I used a TAD Highpower Princeton Reverb replacement transformer. It has the same footprint as the standard Princeton Reverb PT, so no work on the chassis needed. Just to mention that option in case someone in the future would like to build a Blackvibe...

    P. S.: Meanwhile (thanks OCD :D) I changed the NFB like discussed above and put also a RFI suppressor cap at the mains power switch.
     
  4. zorgzorg2

    zorgzorg2 Tele-Meister

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    @EmWeAh What value did you use for the RFI suppressor cap?
     
  5. EmWeAh

    EmWeAh Tele-Meister

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    It's a X2 type cap with 10 nF rated at 305V(AC).
     
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  6. zorgzorg2

    zorgzorg2 Tele-Meister

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    Maybe a stupid question: can I paint the transformers?
     
  7. FenderLover

    FenderLover Poster Extraordinaire

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    Any Colour You Like
     
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  8. EmWeAh

    EmWeAh Tele-Meister

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    Maybe a heat tolerant paint, like used for engines would be good for durability.
     
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  9. BigDaddy23

    BigDaddy23 Tele-Holic

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    Just a quick question: In the absence of the balancing part of the bias circuit, does that AC ground cap need to be there? I thought the bias filter cap does the same job in a regular fender style fixed (adjustable) where this type of master volume is employed.......ie allows total silencing of the amp with the MV turned to zero.
     
  10. sds1

    sds1 Tele-Afflicted

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    Any AC resistance signal to ground is going to be part of the master volume voltage divider and will therefore set a nonzero lower limit to the volume control. To be clear, the signal path to ground is via the bias circuit.

    So yeah the typical Fender bias circuit still needs this cap, but check out the tweed Bassman for an example of a bias circuit that doesn't.
     
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  11. zorgzorg2

    zorgzorg2 Tele-Meister

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    Very good thinking, thanks!
     
  12. zorgzorg2

    zorgzorg2 Tele-Meister

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    20200923_170637.jpg
    Parts are starting to come in!
     
  13. zorgzorg2

    zorgzorg2 Tele-Meister

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    I see @robrob recommends using a light bulb between the wall plug and the amp, but I can only find led-based bulbs here, with low wattage (EU regulations) for powering the amp first times . Would it still work?
     
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  14. sds1

    sds1 Tele-Afflicted

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    Negative. Keep looking, and when you find them -- buy a couple replacements they are real hard to find these days. ;)
     
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  15. D'tar

    D'tar Friend of Leo's

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    possibly try automotive supply stores and ask for rugged service drop light bulbs. They may have them. The move to L.E.D. has rendered the incandescent bulb a rarity! Perhaps we can substitute the load of the bulb with another visual indicator such as a fan motor or similar? Eventually we will need to come up with an alternative.
     
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  16. zorgzorg2

    zorgzorg2 Tele-Meister

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    Look what I found at the bottom of an old storage box!
    20200925_063845.jpg
    A 100w and a 60w!
    I should start with the 60w right?
     
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  17. sds1

    sds1 Tele-Afflicted

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    Why do you say start with 60?

    If you are on 240 there, the math on 100W works out to about 400mA, this is roughly how much current will flow to fully illuminate that bulb. Whereas only 250mA on the 60W.

    As a current limiter either bulb will do, but as a fault indicator you will want a bigger bulb I think. Ideally the lightbulb glows a very minimal amount from normal idle currents, then very bright if there's a short, and so it's all very obvious. The smaller bulbs will glow much brighter at idle.

    You have bulbs now so nothing stopping you from building that limiter now, check out what I mean after you make use on this build and keep your shopping eyes peeled for like a 200-300W bulb...

    Gosh you guys need double the wattage bulbs than us over there then? Hope I'm figuring that right. I use a 150W bulb here on 120...
     
  18. zorgzorg2

    zorgzorg2 Tele-Meister

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    Yes, we are on 240v here, but it's also what goes in the power transformer. So if I limit the power to 100w, it should be what goes in into the amp. If my hv is at say 500v, that means I'll get about 200mA on that wire. And should be independant of whether I'm on 120v or 240v, right?
     
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  19. sds1

    sds1 Tele-Afflicted

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    Yeah you are correct that once you are across the transformers the math becomes normalized no matter the mains.

    But, don't forget you gotta power the filaments too.
     
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  20. robrob

    robrob Poster Extraordinaire Ad Free Member

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    DSM FTW!
     
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