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Pleasurehead

Active member
Joined
Aug 12, 2009
Messages
40
Location
Waterford, Republic of Ireland.
Hi,
I'm fairly new to DIY but am about to attempt a couple of Pultec's. Can anyone tell me how dangerous this would be? I understand that I'm dealing with high voltages but if it's not plugged in I'm relatively safe right?

 
There will be a High voltage thingy going on. I use 2 meters. One on the nasty stuff and always on. And use my other meter for the other stuff. And never got shocked yet. But you better be careful anyway! I always am! Very careful. And if you are unsure of something STOP and ask here first. But really it isn't very hard once ya learn a bit.

John
 
When you start firing up the machine for test runs, always power off and discharge the big caps and measure with a meter before touching anywhere. I learned this the hard way when I was 18 but I got lucky. :)
 
Pleasurehead said:
Ok how do I discharge the caps? Is it just a time thing?
I built a discharging cable with a fat capacitor on it. Its in one of my thread questions. A simple cable connected to a fat cap with low capacitance but high wattage(someone electronically minded confirm this?). One end was connected to an alligator clip and the other end to a probe. I would tie the alligator clip end to ground and the other I would poke capacitors legs with to discharge them, I think it was the positive leg(someone confirm this as well).

Someone could chime in on it, and explain it more technically.

Diagram

ground<---alligator clip-------fat capacitor------probe -->cap leg
 
:eek:

not a cap!

danger danger will robinson!


All you need is a single (roughly) 10k 3watt resistor. Hold against the positive and negative end of your PSU caps. Then double check with multimeter if you are safe.

But you should really have bleeders in the PSU by default. If you need external bleeders, that particular PSU design sucks.
 
Not neccesarily,  if its a high voltage bulb it will grow dim once the voltage bleeds below the rating of the bulb.  I forget the voltage on these units but you might have to use a few different bulbs to get it down to a safe level.(this is not a good idea either way)  If you want to be safe, which is a good idea, then follow peter c's post and the link.  If you plan to continue builds you will need to get used to making little tools for safety.  Without adding a bleed resistor to those big caps will leave you wwith a unit that stays charged for a really long time.

BE SAFE
 
A incadescent lightbuld is a resistive element so this would theoretically work.  (the light bulb resistance for a 60 watt bulb is appx =  V^2/pwr = 220 ohms... sidenote they measure lower when cold)
I use a resistor like described above when working on tube amps (DO NOT USE A CAPACITOR!!)
Always check with a multimeter before working in a high voltage amp!!!
Note also that some capacitors can regain a charge after time... so it is always best to have resistors permanently attached across power capacitors to drain charge. Typically, 220k resistors can be placed across the power caps.
 

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