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This Is Going to Be Different

Discussion in 'Shock Brother's DIY Amps' started by Phrygian77, Oct 22, 2020.

  1. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    PXL_20201022_150516872.jpg

    PXL_20201022_145241520.NIGHT.jpg
     
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  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    So, will that toroidal be on the outer portion of the chassis or does it fit inside?
     
  3. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    It's going to have to go on the outside. I'm going to cut a piece of galvanneal and weld it over the chassis cutout.
     
  4. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    I'm going to do Merlin's 3 gain stage preamp coupled to a single ended EL34. At least, that's the plain for now. I may add another unbypassed gain stage for NFB. Might add 1 tube reverb also.
     
  5. James Knox

    James Knox Tele-Holic Silver Supporter

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    Cool! I be watchin...
     
  6. tubegeek

    tubegeek Friend of Leo's

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    B+ 350, silicon diodes?
     
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  7. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    That's roughly what I'm expecting, but I'd be okay with anything in the 300-350 range.
     
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  8. tubegeek

    tubegeek Friend of Leo's

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    That Antek will put out a little extra, also, since your tube complement and current draw are not very demanding. 350 should be well within reach.

    I mean, you're not going to be pulling 400mA through that thing, are you? Into a SE EL34? I hope? I'm all in favor of bleeder resistors but a 200W light bulb power indicator seems a little excessive.

    :D

    You're aware of the requirements for mounting toroids? No closed loop around the transformer. They usually come with the exact hardware you'll want to use.
     
    Last edited: Oct 22, 2020
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  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    So can the 250v secondaries be wired in series with the common connection used as the CT?
     
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  10. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    Wired in parallel with a full wave bridge.
     
  11. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    It's overkill, but probably 50VA wouldn't be enough. I could go to a 12 wattish push pull also.
     
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  12. tubegeek

    tubegeek Friend of Leo's

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    Yup.

    You can do whatever the heck you want! If you connect the 2, 250's dot to dot, they're parallel, 250 V @ 400mA. If you connect them dot to no-dot, they're series 500V CT @ 200mA also known as 250-0-250.

    It's the same kind of options as the primary has, basically.

    If you want to get crazy, put one of the 120s in series with 250 and 250, you'll have 620V at some lesser current, (100 VA is 620 @ 160mA, but 160 mA would need to be derated somewhat for using only the single primary connection.)
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Any advantage choosing series vs parallel, especially in a low ampere draw such as this build?
     
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  14. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    400mA AC
     
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  15. tubegeek

    tubegeek Friend of Leo's

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    Hmm. Good question. You're thinking - full wave/ 4 diode bridge vs. just full wave using the center tap & two diodes.

    Well, I guess there's the extra diode drop of .7V in the bridge config, that'd matter in a lower voltage project perhaps.

    If you were worried about the large inverse voltage across your diodes, I suppose the bridge would split it between the two. So easier on the diodes/save 2 cents using lower rated parts I suppose.

    That's gotta be a question that comes up in power supply design chapters. In an in-between voltage like this ( not 10 V not 1000V) I wonder too... none of those reasons above seem the least bit compelling.
     
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  16. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    That is what I thought a couple of parts. No particular advantage with the amperes either. It would be able to provide ~200mA.

    Good to know.:)
     
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  17. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    With the secondaries in series, and a full wave rectifier, I think that gives you 200mA DC. In parallel with a bridge rectifier, you get the RMS of the 400mA AC rating, so about 250mA.
     
  18. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    For one configuration to supply fewer mA, the loss would create heat. That is not the case.

    In series each of the two halves can supply 200mA. When rectified, one half handles the forward direction (let's say the top of the waveform). The other half handles the reverse direction (let's say the bottom of the waveform).
    In the end it is 200mA on each side alternating back and forth.

    In parallel it can supply 400mA. When rectified the waveform is split in two. The top of the waveform and the bottom of the waveform.
    In the end it is 200mA on each side alternating back and forth.

    Same same.
     
  19. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    With a 400mA rating at 250VAC, rectified that should equate to 400 x .637, 254.8mA. I said about 250mA. Are we misunderstanding each other?
     
  20. tubegeek

    tubegeek Friend of Leo's

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    Hammond power supply design guide.
     

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