Safety First

High VoltageAs Bon Scott of AC/DC said “High voltage rock ‘n’ roll”, these two items go together had in hand in guitar amplifier building.
But really, the Low Voltage can be extremely dangerous because in the end it is the current that is the one that kills.
We are getting shocked daily with 27-30,000 Volts, sometimes not even noticing – for example when we pull off or on our synthetic sweaters or getting out of the car and touch the door handle on a very dry day.There is a Golden Rule on safety when it comes to guitar tube amplifier building:

Always have one hand in your pocket when poking inside and amp chassis!

The reason is that you can still have one hand available to pull the power cord out of the outlet. Another important advice:

USE YOUR COMMON SENSE! (don’t be dumb! 🙂

Don’t touch things you suspect having live lethal potential. You wouldn’t touch a hot pot sitting on the stove if someone mentioned that to you, right? Well, I AM MENTIONING that:


(you can use that as a disclaimer)

Here is a list that you should go through to learn about electrical safety:
1. Use a good quality power cord and don’t mess with the plug’s connections.
2. Stay away from 3-to-2 prong adapters.
3. Make sure your house has grounded outlets. Use an outlet tester.
4. Don’t improvise. We do that in jazz or cooking.
5. Make sure your work area is dry and preferably carpeted. It is wise to wear snickers with a thick rubber sole.
6. Install a ground fault circuit interrupter (GFCI) and use that as the outlet for testing amps.
7. For the life of me – have your area well lighten. Many faults can be overlooked in shadowy areas.
8. Use a chop-stick to poke around your components. NOT YOUR FINGER!
9. Electricity still lingers around for many days even after you unplugged the amp. The filter electrolytic can keep a good dosage of lethal voltage. Use the Filter Capacitor Bleeding Trick to uncharged the capacitor explained later.
10. Use a Voltage Test Screwdriver w/ Neon Lamp to test for any suspecting parts that might have live voltage potential. I use this tester ALWAYS when I power an amp up by first touching the chassis with it to see if somehow has live voltage. That should be your preliminary test.

Grounded AC Plug Color Code (USA)
The common color code code to recognize each wire’s role in a grounded AC plug (USA) is:

WHITE: Neutral
GREEN: Ground

Filter Capacitor Bleeding Trick
I use this cheap trick to make sure I squeeze out every possible leftover potential from the filter capacitor:

Considering that the amp-to-be-serviced is working, strike a power chord on your guitar at a pretty loud volume, preferably a A minor 🙂 then immediately hit the ON/OFF switch to off. You will hear your sound trailing away to nothing as a result of the charge being bled out of the filter capacitor to a voltage that’s safe to handle.

To be sure, you can also check the leftover voltage in the filter cap with aVoltage Meter set to the (at least) 500V range.

Having these rules in mind together with a healthy respect for electricity, will give you a surprise free guitar amplifier building.

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