# Cap???



## Metal#J# (Jan 1, 2007)

If you turn off an amp without putting the amp in standby first, will doing this empty the charge in the caps. I think that I read this on this forum a log time ago but I just want to confirm it.

Thanks,

J


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## Wild Bill (May 3, 2006)

Metal#J# said:


> If you turn off an amp without putting the amp in standby first, will doing this empty the charge in the caps. I think that I read this on this forum a log time ago but I just want to confirm it.
> 
> Thanks,
> 
> J


Maybe yes, maybe no!:smile:

You can't have a definite answer because it all depends on the circuit of a particular amp. It's always been good practice to design your power supply with what are called 'bleeder resistors' that will allow a tiny bit of current to flow to ground. Too little to affect the amp's operation but when the amp is turned off it's enough to empty the capacitors after half a minute or so.

Some designers didn't do this, especially a lot of the modern designers. So the amp can hold a charge for a LONG time, maybe months! Turning the standby switch doesn't help. If the tubes are off they won't draw any power, period.

Any smart tech will discharge the caps himself every time he goes to work on an amp, especially if he's gotten a jolt a few times!:smile:

:food-smiley-004:


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## nonreverb (Sep 19, 2006)

Wild Bill said:


> Maybe yes, maybe no!:smile:
> 
> You can't have a definite answer because it all depends on the circuit of a particular amp. It's always been good practice to design your power supply with what are called 'bleeder resistors' that will allow a tiny bit of current to flow to ground. Too little to affect the amp's operation but when the amp is turned off it's enough to empty the capacitors after half a minute or so.
> 
> ...


Words to live by (pardon the pun...)


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## Metal#J# (Jan 1, 2007)

Thanks Bill,

:food-smiley-004:

J


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## J S Moore (Feb 18, 2006)

How about a JCM 800? I thought I would ask before I go poking around in mine.:smile:


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## bcmatt (Aug 25, 2007)

J S Moore said:


> How about a JCM 800? I thought I would ask before I go poking around in mine.:smile:


My JCM 800 always gives an exciting spark from the cap cans if I want them to. I would definitely ground them out (using a resistor for less drama).


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## mhammer (Nov 30, 2007)

Aw, but then you don't get to see "the blue lights".

Gents, what would you consider to be a useful visual indicating device to determine when caps are sufficiently drained? For example, are there commercially available things one might buy at Caadian Tire? things you can cobble together with a pair of probe contacts from Radio Shack and a light bulb?


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## greco (Jul 15, 2007)

mhammer said:


> Aw, but then you don't get to see "the blue lights".
> 
> Gents, what would you consider to be a useful visual indicating device to determine when caps are sufficiently drained? For example, are there commercially available things one might buy at Caadian Tire? things you can cobble together with a pair of probe contacts from Radio Shack and a light bulb?


Two wires with probes/aligator clips and a light bulb (or power resistor) can be built.

The cap should be checked with a multimeter after it has been drained.

Dave


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