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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reilander Pickups
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com Reilander Pickups
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Discharge filter caps????

Discussion in 'Amp Central Station' started by rich602, Aug 28, 2010.

  1. rich602

    rich602 TDPRI Member

    47
    Aug 16, 2010
    Tool Shed, CO
    Discharge filter caps. What's that mean?
     
  2. gaddis

    gaddis Tele-Afflicted

    Aug 22, 2004
    New York
    The caps in the power supply off your amp retain a high voltage, even after the amp is turned off. Prior to working on an amp, it's important to discharge this voltage so that you're not putting yourself in danger.
     
  3. wharfrat

    wharfrat TDPRI Member

    32
    Oct 19, 2008
    San Francisco, CA
    The filter capacitors can store a charge for a long time after the power is turned off,
    so it's a good idea to discharge them by shorting across them after the power is off and before sticking your fingers in there.
     
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  5. T Prior

    T Prior Poster Extraordinaire

    Mar 17, 2003
    Charlotte NC
    It's not a good idea to short across the caps, use a 100 or 150 ohm, 10 watt resistor and clip the + side to ground. Another way to discharge 70% or 80% of the charge is to keep playing your guitar, chords, while turning the power switch off, leaving the standby on.
     
  6. polymolly

    polymolly Tele-Meister

    352
    Apr 30, 2008
    Portugal
    I always connect an alligator clip to pin 1 of the first preamp tube and the other end to the chassis, with the amp disconnected from the wall, the turn the amp on and leave it like that for a few minutes. Don't know if it is the best way, but I'm still alive :S
     
  7. celeste

    celeste Friend of Leo's

    Age:
    55
    Jun 24, 2006
    Maryland
    That is fine if you know that the first preamp tube has a plate connected to pin 1. That would not work for say a Vox with a EF86
     
  8. polymolly

    polymolly Tele-Meister

    352
    Apr 30, 2008
    Portugal
    I do know, but thank you for protecting my fingers from getting burn!
     
  9. Billm

    Billm Friend of Leo's

    Mar 26, 2008
    New Jersey
    If your amp has a standby switch, leave it in "play" position when you turn the amp off. If the amp is fully warmed, enough to play through, it will self-discharge when you turn it off.

    And as Ronnie Reagan said, "Trust, but verify." Check from ground to the + side of the filter caps with your meter. You will usually see a 10-15 volt residual charge on the caps. This is harmless; it's the chemistry in the electrolytics. You can discharge it with a jumper wire if you want or just ignore it.
     
  10. rich602

    rich602 TDPRI Member

    47
    Aug 16, 2010
    Tool Shed, CO
    What about solid state amps. I have a Vox Pathfinder. Thanks
     
  11. Ronsonic

    Ronsonic Tele-Afflicted

    Solid state amps generally discharge themselves pretty well. Generally.

    Always just take a meter and check. Just check and discharge as needed.

    A light bulb with clip leads attached, like the one you clip in place of a fuse for testing also works well.
     
  12. 6x47

    6x47 Tele-Holic

    804
    Mar 28, 2007
    Northern ON
    I use the method advocated by Doug Hoffman; with amp on and strumming guitar, pull the plug while continuing to strum. You can actually hear the volume die as the caps drain and it gives you a pretty good idea how strong your caps are once you get the hang off it.

    With weak caps the sound goes almost instantly, while strong caps give you noise for a while.

    I always check with a meter the first time I do this with a amp.

    I find this the quickest and easiest method for draining the caps on an assembled amp.
     
  13. Billm

    Billm Friend of Leo's

    Mar 26, 2008
    New Jersey
    There's no difference between pulling the plug and turning the amp off. Strumming the guitar is also not a necessary part of the process. The amp will discharge in 30 seconds or less either way.

    Of course, you should unplug it before you take it apart.
     
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