Monday, September 27, 2010

PUBLIC SERVICE ANNOUNCEMENT

A WORD ABOUT HIGH-VOLTAGE SAFETY
Many people don't know that working in tube amps can be extremely dangerous. There are LETHAL voltages inside these things when they are powered up, and for a time after they are powered down, even days. It is entirely up to you if you wish to risk your life working inside one of these, otherwise refer to a qualified and experienced Amp technician.

This is not a hobby for the faint of heart, but if you commit a few safety rules to memory, then you will live a long healthy life without getting electrocuted or bitten by a nasty jolt due to carelessness:

* ALWAYS WORK ONE-HANDED whenever working inside an amplifier or other tube-based electronics. This does not matter if it is powered up or not. The Capacitors can hold a charge for a long time, unless discharged properly. Once you can confirm that your Volt-Ohm-Meter measures 0 Volts DC from the B+ to Ground, then it is safe to work with both hands after unplugging. Otherwise, shove your non-dominant hand into your back pocket, and leave it there.

* NEVER WORK TWO-HANDED if you are not sure if your amp still has a charge. Since if you make a circuit between your hands, the current will flow straight across your heart. I can't reiterate this point enough.

* OBSERVE PROPER POLARITIES of components, otherwise you risk fires or or exploding capacitors in your hardware...And you will weep if you destroy an expensive piece of Iron (transformers) or pop expensive tubes.

* CAREFULLY CALCULATE YOUR MOVES AND ACTIONS before attempting to probe a hot circuit. Don't be careless. Use an insulated probe like a glass rod, fiberglass rod or dry wooden chopstick.

* A "BLEEDER RESISTOR" CAN SAVE YOUR LIFE. This is simply a 100KΩ 1-watt resistor attached to the High-Voltage B+ rail at the first stage (the Plate of Tube 'V1'), and grounded to the input jack's ground. After you power down your amp and unplug it, this will slowly bleed all the remaining current from the capacitors, typically over a period of 2-10 minutes. Confirm afterward by measuring the B+ rail to ground that you get 0 Volts DC before attempting to work inside of it.

(In progress, stay tuned for updates to this post)

9 comments:

  1. I'm guessing it would hurt pretty bad to have a lot of voltage flowing through you :(

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  2. Interesting stuff. Where'd you learn?

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  3. Just about every serious Amp site and Electronics book on Tubes has the same disclaimer. AX84 has the same disclaimer at the beginning of each .PDF they have available. They don't mess around, and anyone worth their salt takes this warning deadly serious.

    It's not even the Voltage you need to worry about most, it's the Current. Most amps have anywhere between 50mA to 300mA of current running through the High-Voltage rail.

    Only 15mA is enough to stop your heart.

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  4. I think I'll just leave this stuff to lads like you.

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  5. DANGER DANGER, HIGH VOLTAGE, WHEN WE KISS, WHEN WE TOUCH.

    Cawlin's Twitter!

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  6. Glad you have the sense to give safety tips in correspondence with what you post on your blog :]

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  7. but but don't people want to be human circuits with 2 hands :D, jk -_-

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  8. this is a good post that makes me want to come back for more

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  9. If I ever go copper stealin I'll heed your advice.


    I'm just kidding, I'm white.

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