Guitar Tube Amp

Step 1: Danger, Will Robinson, Danger!

Here's the standard disclaimer:

This is dangerous, high voltage stuff. OK, it's not "High Voltage," technically, but it's high enough to kill you. The power supply in this projects kicks out 200V, which is plenty, with startup spikes near 240V or more...

Don't believe it when they say "it's not the voltage, it's the amperage that kills you"--because it's both. Amps AND volts together dictate the danger level. If it were amps alone, then even a AA battery can supply many times what's needed to stop a human heart. The volts do the "pushing," and overcome the natural resistance of your skin. And there's plenty of current available to harm you in any tube audio amp...

Remember:
--Always drain the power supply filter caps before touching the circuitry.
--Always unplug the mains cord before working.
--Double-check (with a VOM) to be sure the filter caps are drained.
--DON'T mess with this stuff unless you have a decent understanding of the dangers.
--DON'T mess with this if you believe you know EVERYTHING about high voltage, and think that makes you immune to electrical shocks.

Comments

[REA]

isnt it the amps (lol pun!) that kill you, not the voltage?

[ElJefeUno]

Anything above 40 volts is generally considered "high voltage", as it's enough volatage to break down your skin's inherent insulation and allow current to flow across your heart high enough to kill you. I've built tube amps, and I recommend to anyone aspiring to build on that they use extreme caution while working with them. Discharge all caps before working on it (as stated above), and take great care when using a multimeter to troubleshoot. I personally use "gator clamps" when checking high voltages, so that I can do it hands off and not risk my life.

[dickweed101us]

I KNOW THIS IS OLD BUT, This is from Wikipedia The International Electrotechnical Commission and its national counterparts (IET, IEEE, VDE, etc.) define high voltage circuits as those with more than 1000 V for alternating current and at least 1500 V for direct current, and distinguish it from low voltage (50–1000 V AC or 120–1500 V DC) and extra low voltage (<50 V AC or <120 V DC) circuits. I just dont like when someone goes saying something that they dont know anything about...

[sonofkikkoman]

but there is a big difference in 40vac and 40vdc

[gmoon]

Thanks, good comment.

[mattzerah]

Yes, you are correct in saying that its a combination of amps and volts, but when it comes down to it, its the amps that actually determine if you die or not. The reason a AA battery doesn't kill you is your body provides enough resistance to bring the amps down to a safe level. There are also cases (with car ignition) where thousands of volts may not kill you. Thats because the amps that are produced by the ignition are not enough (although its border line, dont try that at home, people have died from car ignitions, but some people havn't). The reason home voltage kills you is it runs at 10A (well, in australia it does) and the amount of resistance that your body provides to that just is not enough to bring it to safe levels. I'll stop rambling now and read the rest of the story :) Great project!

[gmoon]

Lets just say it's a different way of saying "be careful."

The reason a AA battery doesn't kill you is your body provides enough resistance to bring the amps down to a safe level.

That's another way of making my point. For a fixed resistance, increasing the voltage drives more amps. Take any 6V motor, and measure the current draw. Now increase the voltage outside it's operating range, say to 12V. The amperage increases and the motor burns out.

Yes, the amps killed the motor. But it was the extra voltage that drove those amps through the motor coils. So you really need to think about the whole Ohms Law equation, not just amps and not just resistance...

(Plus the transconductance of human skin is not linear--skin shows less resistance as voltage rises, not a linear change dictated by "Ohms Law," but an actual reduction in resistance, which implies that voltage is quite important, too.)

[smeezekitty]

FYI most 6 volt motors work on 12 volts ;)

[gmoon]

None that I've bricked...

[planetmuncher]

whats funny, when i was taking apart an old amp i got for free, i left it plugged into the wall, i touched that amplifier....F***! i was right next to my dad he was laughing at me yeah always unplug it!

[titsanonymous]

how do you drain the electricity from the amp

[gmoon]

The current is stored in the "filter caps," which are connected after the power supply rectifier. Essentially, you need to drain those capacitors; shorting them by connecting the leads together, or by connecting the positive (+) cap terminal to the GND.

There's more info here, on my amp rebuild project.

[n0ukf]

If you short across the caps with a wire (or tool) you'll get a high current snap as it arcs. If you use a resistor (perhaps 1K, at least 1W) it'll take a little longer to drain but it'll drop the arc intensity.

[gmoon]

Thanks! (the link above also mentions using a jumper / resistor combo:)

-- OR jumper the positive (+) lead of each large cap to GND for several seconds. A jumper with a built-in resistor (10K or so) will help prevent sparks here...

[arsenaldb10]

Anyone have an idea on the maker of that guitar?

[wasteofspacester]

Try Eastwood Guitars. They do a lot of classic yet unusual designs.

[arsenaldb10]

That's exactly who makes it. It's called Saturn. Thanks!!