Discharging.wmv

How to discharge a tube amplifier easily. Safely remove the charge from the power supply capacitors. If you would like to comment, please use this page:
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>> The purpose of this video is to dispel some myths about discharging a tube amplifier.

I am using a vendor blues junior here as an example,

but it applies to any other tube amplifier.

As you can see, I've got a volt meter,

hooked up to the main power supply filter capacitor,

and it's measuring four volts right now,

which is just a chemical residue in the electrolytic capacitor,

it doesn't really mean anything,

it's just a byproduct,

not at all important.

I'm going to turn the amplifier on and then turn it off quickly.

Now, you see that it's going down and went up to

about 330 volts and it slowly going down 266,

265 and it's discharging slowly just leaking

through various components inside the amp and

natural leaked down that you get with electrolytic capacitors,

but that's more than enough voltage to knock you on your tail,

so you don't want to mess around with that.

Now, one way to discharge a cold amplifier like this is with

a simple jumper wire with a 10,000 ohm resistor 10K resistor held in one clip.

If I touch that, actually anywhere around here,

it'll take the voltage down rather quickly, 8460, 2216, 1812,

anywhere in the power supply will take it down.

Now we're down to two, one volt.

So, that's a very safe and easy way to discharge any amplifier.

The 10K resistor only prevents sparking,

I could touch it directly but I would get an arc,

the 10K resistor slows down the discharge and makes it easy.

Now, let's do the same thing again,

we'll bring the amp up to full operating voltage,

which is in this case,

we see 347 volts, 348,

and as the two tubes warm up,

you'll see that the amp will actually drop in

voltage because the tubes will start conducting.

Now it's down to 333, 334, 330.

So this is a normal voltage that you would see in a blues

junior with normal operating conditions.

Now, you can play through the amp, it's live.

Now, if we just turn it off,

remember we turned it off before when the amp was cold and nothing happened.

Now, I'm going to turn it off and watch how quickly the voltage goes down, 50, 42,

26, 16, faster than it did through the 10K resistor,

three volts, two volts.

Why? Because it's conducting through the ELAD force primarily and the other tubes,

but these guys are always using a lot of current all the time.

So, simply turning off a warm amplifier is all you have to do to discharge it.

So, now we can strum it,

nothing is coming through the amp,

and this is ice cold,

I can touch it with confidence,

know that I'm not going to get knocked on my tail or anything like that.

So, what about the old myth of having to strum the guitar while you're discharging?

Let's take a look at that, we'll bring it back up to operating voltage again.

So, we're stable at around 334 volts,

and we have a normal sound,

and now we'll strum while we're discharging,

the powerful E chord there,

and you notice that it discharged in exactly the same way as it did when we didn't strum.

There is no reason to actually strum the guitar,

that's just one of those internet myths that gets perpetuated.

The only thing that the strumming does is

confirm that all of the current is gone from the tubes,

but it can be deceptive,

if you had turned the amplifier on and off quickly and these were cold tubes,

it would hold a charge and it wouldn't play when you strummed it.

So, the safest thing to do is always to bring the amp up to full operating temperature,

so you can play through it and simply turn it off,

that will always discharge it all the way down.

Don't put it in standby,

don't do anything else with it,

and you can play if you want to confirm,

as the sound fades out,

you know that it's being discharged and that's all there is to it.