[sdiy] Tube amp cap discharge tool?

[René Schmitz]

Hi Michael,

> Can anyone give me a quick recipe for a safe tube amp capacitor discharging 
> tool?  That is, something I can use to discharge the voltages found on filter 
> caps in tube amps after you turn the amp off, so it will be safe to stick my 
> hands and tools in there to work on them.  I'm guessing that I need something 
> like a fairly large value, high wattage resistor connected on one end to a test 
> clip that I hook onto chassis ground, using the other end of the resistor to 
> touch the hot side of the charged-up capacitors to shunt the charge to ground, 
> but I'd like to know for sure if this is the right way to do it, and if so, 
> what value should I use for the resistor (both resistance and wattage).  Any 
> other tips about precautions, procedure, or techniques would be much appreciated. 
>  Sorry to be such a pussy about this, but for some odd reason, I am not so 
> much in the mood for electrocuting myself today.


Best thing is to put bleeder resistors across the caps *permanently*. 
Say 33-100k or so, power handling depending on the voltage P=U²/R. Then 
you can always work safely after a couple of minutes (tau=R*C, takes 
several tau's until the voltage is safe though). The thing is that high 
voltage caps can charge them selves up again, due to dielectric absorption.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159