HT Bleeder Idea

Discussion in 'Shock Brother's DIY Amps' started by andrewRneumann, Jun 10, 2021 at 11:36 PM.

  1. andrewRneumann

    andrewRneumann Tele-Holic

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    Has anyone ever contemplated incorporating an HT bleeder like this (with a fuse of course)? Pros / cons? BLEEDER (2).png
     
  2. Lynxtrap

    Lynxtrap Tele-Holic

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    Not sure what that is supposed to accomplish...?
    IMO no wiring should be based on the assumption that neutral will be neutral at all times.

    In many countries it is totally out of the question.

    [​IMG]
     
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  3. NTC

    NTC Tele-Holic

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    Maybe if you connected the bleeder to the ground lug, but there are still no guarantees it is ground. And again, why? Unless you plan to open and work on the amp every time after it is turned on, you really don't need to drain the caps at power down.
     
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  4. 2L man

    2L man Tele-Meister

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    Both a bleed and a filament lift can be done using the same circuit which contain two resistor voltage divider and one electrolyt over bottom resistor.

    Between power transformer primary and secondary there shouldn't be ANY CONNECTION because it is electric risk!
     
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  5. andrewRneumann

    andrewRneumann Tele-Holic

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    Exactly. I am contemplating this for a test rig. I spend so much time with alligator clips and multimeter bleeding down the HT, wanted to find a quick but SAFE way to do it repetitively.
     
  6. andrewRneumann

    andrewRneumann Tele-Holic

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    That’s a good point and an easy one to forget.
     
  7. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    Look at the bottom of this page (http://www.valvewizard.co.uk/OtherStuff.html) for some ideas with LEDs. Idea 4 might be a method to easily see the caps drain.

    (Theoretically?) You could use a switch that switches hot & neutral _and_ the bleeder to ground. Or use a separate switch for the bleeder.

    Btw, we've got the same wall outlets as Lynxtrap showed here in The Netherlands.
     
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  8. Nickfl

    Nickfl Friend of Leo's

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    Is there a reason you don't want to use a normal bleeder resistor across the filter cap?
     
  9. wallybob

    wallybob TDPRI Member

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    I think that the main electrical flaw in this circuit is that in order to discharge the filter caps, a bleeder circuit would have to involve the neg side of the filter caps. Your switch is connected to the line neutral. Neutral is not connected to cap neg ground in any of the amps I've ever built. Of course, this point is secondary to the fact that there are much more convenient ways of achieving your requirements.
     
    Last edited: Jun 12, 2021 at 5:11 PM
  10. andrewRneumann

    andrewRneumann Tele-Holic

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    I'm a sucker for some cool LEDs! They make you look like a genius to the common folk. Of course, VW is a genius... so he's allowed to have LEDs.

    The goal of this is bleed fast and bleed often. So would like to use a low resistance and not have a separate switch. Your idea of a 3 pole switch is genius. Something like this maybe?

    BLEEDER (4).png
    CORRECTION: It would be a 3PDT switch, not a 3P3T.
     
    Last edited: Jun 12, 2021 at 4:43 PM
  11. andrewRneumann

    andrewRneumann Tele-Holic

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    For speed. I just want to have it drain super fast when I throw the switch, double check it with the meter, and get to noodling around in there. Again, this is for testing/modification. The final amp would have the normal bleeder everyone is familiar with.
     
  12. andrewRneumann

    andrewRneumann Tele-Holic

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    After looking at it some more and reading the group's input, I think the main safety flaw is that if you unplug the amp while it is running and then turn off the switch, HT is then present on the neutral blade of the plug. Revised drawing above should solve that problem.
     
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  13. Mexitele Blues

    Mexitele Blues Tele-Afflicted

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    I used a 220k to ground directly after the rectifier. By the time I could grab my multimeter and check the caps, they were down to single digits, and the act of checking drained the remainder. I don't think there's much time to be saved.
     
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  14. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    That is probably with (hot) tubes. They conduct way more than the resistor.

    For a (total) capacitance of 50uF, a 220k resistor drains the caps to ~60% (of the charge and thus voltage) in 11 seconds. And a further 11s to get to 60% of that (so 36% of the original voltage).
     
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