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Tube amp building and use safety!

(Version 0.2 03/30/2000)
--By Gino "rebel420" Iorfida
giorfida@drifteramps.com

A. Forward

There is nothing else in the world like the sound of a good tube amp. Some even say the amp is the most important part of a good electric guitar tone. This document is not intended to be inclusive of everything out there, nor is it a substitute for common sense. Think of it as a starting point, rather, of some do's and don'ts that one should keep in the back of their mind.

B. Use tips

STANDBY - The standby switch on an amp serves 2 purposes. The first is that it allows the tubes to warm up before being slammed by the high voltage they need to operate. Proper use here will ensure your investment is around for the next gig. The second purpose is that it will keep the tubes warm, yet allow you to mute your amp, and rather save the tubes further by relieving them of some stress while you are changing guitars, or taking a 5 minute break. It is there for a reason. USE IT whenever you fire your amp up. Turn on the amp, let it warm up for a few minutes, then flick the standby. You THEN are ready to go! When powering the amp down, however, most will agree that it is best to just power the amp off without going into standby first. It lets the capacitors in the amp drain gracefully.

RETUBING - Its ALWAYS better to change your power tubes before they go on you. When a power tube fails, a lot of times it takes other components out with it. How often should you retube? There is no set-in-stone amount of time they last, since there are many factors affecting tube life. A rule of thumb, however is if you gig more than a few nights a week, every year you should retube at least. If your amp doesn't seem to have the power that it used to have or just sounds dull and lifeless, chances are its time to retube. Preamp tubes tend to last much longer. In fact, there are amps out there today that have been used heavily for 20 years or more with the original preamp tubes. ALWAYS BIAS YOUR NEW TUBES! IF YOU CAN'T DO IT YOURSELF, TAKE THE AMP TO A QUALIFIED TECH!

IMPEDANCE - ALWAYS follow the rated impedance of your amp. If you have a selector switch, make sure it is in the proper position for the speaker load you are using. The only exception to this is if you have an amp that uses 4 power tubes such as a Twin or a Marshall, and you want to reduce the power by pulling 2 of the tubes, ALWAYS double the speaker load compared to what the setting says: for example, if you pull 2 tubes on your Marshall (either the inside pair or the outside pair, never 2 from one side or the other), and you have a 16ohm cabinet, you must set the amp for 8ohms. NEVER UNDER ANY CIRCUMSTANCE RUN THE AMP WITHOUT A SPEAKER ATTACHED. YOU WILLDAMAGE YOUR AMP!

COOLDOWN -It is always a good idea to let your amp cool down for a while before moving it, or messing with the tubes. Your tubes will last longer, and you will avoid some serious burns. Wear welding or oven gloves or use a hotpad if you must handle hot tubes!

LOUDNESS - Your ears are vital as a musician. If you are going to be playing your new creation at loud volumes (even 5-watt amps can be painfully loud!!), wear earplugs, use a good quality attenuator such as a Marshall Powerbrake or a THD HotPlate. Tinnitusis a real disorder. Please, save yourself from this.

TUBES - NEVER use tubes other than what the amp was designed for, unless you know that it is safe. When in doubt, check with a qualified technician. And ALWAYS rebias!

FUSES - Fuses are your friends. NEVER UNDER ANY CIRCUMSTANCE REPLACE A FUSE WITH ONE WITH A HIGHER RATING. OR REPLACE A FAST-ACTING TYPE WITH A DELAYED-ACTION (SLO-BLOW) TYPE. AND NEVER NEVER NEVERREPLACE A FUSE WITH ONE WRAPPED IN FOIL OR OTHER DEVICE TO DEFEAT A FUSE. THESE ARE HERE TO PROTECT YOU IF SOMETHING GOES AWRY. USE THEM!

VARIAC - Sure, Eddie Van Halen made use of a variac to get his tone. A variac is a VARiable AC supply. Running an amp at a higher voltage than it is designed is a sure way to ruin the amp. Likewise running at a lower voltage can cause serious problems due to the heaters in the tubes running too cold, which can lead to cathode stripping, which leads to shorter tube life, which can sometimes cause other problems. The best way to use a variac is NOT to use one. A variac is to only be used for repair and building purposes as a piece of bench test equipment. EVEN if you use a variac to regulate your line voltage, which is a good thing seeing how line voltage can vary from place to place AND most vintage amps were designed to run at a slightly lower voltage (110VAC) versus what most line voltage is now (120VAC), having one on stage is just asking for your drummer, or anyone else nosing on the stage to play it and see what kind of fun they can have.

GROUNDING - If your amp has a 2-wire power cord. PLEASE replace it with a 3-wire type! You will save yourself a lot of pain in the future. Likewise, NEVER EVER remove the grounding prong of a 3-wire cord! If you absolutely must use a 2-wire outlet, use a 2 to 3-wire adapter, and run the ground lug to a suitable ground point. Failure to abide by this CAN and WILL cost you your life!!

C. Building and repair safety

All tube amps possess lethal voltages. They CAN kill you! If you are not qualified to work on an amp, then by all means take it to a qualified technician! Don't prove Darwin right and end up eliminating yourself from the gene pool. Better be safe than sorry!!! TO PUT IT SAFELY YOU COULD DIE IF YOU MESS UP!!!

Ok, disclaimer aside, building your own tube amp can be the most rewarding experience, and knowing how to service one as well. It is especially nice to know how to bias your amp, so if/when a tube dies on stage, you can be up and running in a few minutes. Although this experience is rewarding, it CAN be dangerous. BUT you and only YOU can make it as safe as driving a car, as long as you follow a few simple guidelines. This guide will not take the place of knowing as much as you can, but it's a good reminder.

DISCHARGING CAPACITORS - the filter capacitors in an amp will retain a charge for quite some time after the amp is shut off and unplugged. It is a good idea to make sure your amp is safe to work on. My personal preference is to take a wire with an INSULATED alligator clip on each end. Clip one end to a good ground point, and the other to one of the plate leads for the first stage preamp tube. Another method would be to put a 100k, 5 or more watt resistor in line of these 2 clips and put one end first to ground, then the other to the filter caps themselves. NEVER SHORT THEM OUT DIRECTLY!

BE THE ONE-ARMED TECHNICIAN - there will come a time when you have to work on a chassis that is running. When doing so, if possible clip one of your meter's test leads to ground, and use only 1 hand to probe the circuit, keeping the other in your pocket etc. That way if you DO take a shock, your heart is not in line of the path of least resistance -in one arm and out the other. When you ABSOLUTELY must use 2 hands, be EXTREMELY CAREFUL, and use common sense, but PLEASE try to avoid these situations!

NEVER WORK WHEN YOU ARE TIRED/FATIGUED/INTOXICATED - this should go without saying, but I'm saying it anyways. When you are in any of these conditions, your reflexes are slower, and you would be more likely to make a fatal mistake. Ask yourself this test--would you be willing to take your driving test with a police officer in your car in the shape you are in? If you answer no, then DO NOT poke around in your amp!

FUSES - Fuses are your friends. NEVER UNDER ANY CIRCUMSTANCE REPLACE A FUSE WITH ONE WITH A HIGHER RATING. OR REPLACE A FAST-ACTING TYPE WITH A DELAYED-ACTION (SLO-BLOW) TYPE. AND NEVER NEVER NEVERREPLACE A FUSE WITH ONE WRAPPED IN FOIL OR OTHER DEVICE TO DEFEAT A FUSE. THESE ARE HERE TO PROTECT YOU IF SOMETHING GOES AWRY. USE THEM!

GROUNDING - Along with fusing your power source, grounding is just as vital an issue. NEVER use a 2 wire cord with the dangerous "ground" or "polarity" switch. A 3-wire cord of at least 14AWG is recommended. The cord should be connected that there is a direct path from the chassis ground to the mains ground. FYI, the GREEN wire is generally the ground wire, WHITE is the neutral, which in MOST electrical systems is bussed to ground, and the BLACK wire is the voltage. Without a ground connection, YOU may become the path of least resistance if something goes awry.

COOLDOWN -It is always a good idea to let your amp cool down for a while before moving it, or messing with the tubes. Your tubes will last longer, and you will avoid some serious burns. Wear welding or oven gloves or use a hotpad if you must handle hot tubes!

IMPEDANCE - ALWAYS follow the rated impedance of your amp. If you have a selector switch, make sure it is in the proper position for the speaker load you are using. The only exception to this is if you have an amp that uses 4 power tubes such as a Twin or a Marshall, and you want to reduce the power by pulling 2 of the tubes, ALWAYS double the speaker load compared to what the setting says: for example, if you pull 2 tubes on your Marshall (either the inside pair or the outside pair, never 2 from one side or the other), and you have a 16ohm cabinet, you must set the amp for 8ohms. NEVER UNDER ANY CIRCUMSTANCE RUN THE AMP WITHOUT A SPEAKER ATTACHED. YOU WILLDAMAGE YOUR AMP! AN AMP WILL GET DAMAGED JUST AS QUICK ON THE TEST BENCH AS IT WILL ON STAGE! Use a dummy load if you have to.

DARKNESS - there are times that you are going to work with the lights out, so as to see arcing, or to notice the glow on tubes. Before you turn out the lights, plan what you are going to do, know your work area, and use a softer light if you have to so you don't make mistakes. To quote something I've seen elsewhere on the net, I think it was coined by R.G. Keen, but it is a statement that sticks with me, and if you can remember it as easily, all the better!: LETHAL VOLTAGES ARE JUST AS DANGEROUS IN THE DARK.

CHILDREN, PETS AND OTHERS - Your workbench is not the place to let the children or the pets play. The lethal voltages will be even more lethal for them! ALWAYS make sure you unplug your work, and even lock the room when you are away from it. Remember, death IS permanent! You wouldn't let your children or pets play in the middle of the freeway, nor should they around an open chassis.

HAIR AND CLOTHING - both can be good conductors of electricity. Keep them away! They also have a hard time dealing with power tools and soldering irons! While we are on the topic of clothing, wear the right clothes. Shorts can be bad when soldering, or other hot items, wear pants, it could save you some grief. As one who's had molten solder splashed on body parts, I know from experience, it is NOT fun. Tubes can be just as hot, USE a rag or gloves, and they too can hurt on the legs. Pants will also give you that extra margin of safety, if say you are probing the plates of your tubes for voltage, and by some freak of nature, the one you had clipped to ground came loose and hit your leg. That probe is carrying the full potential of what you are probing, which in some cases could be over 700volts!! Sure, the pants probably won't help you here, if the tip pierces them, but it will give you that extra chance! Safety goggles should be worn when using power tools. Yes, this is obvious, but many people tend to neglect this! ALSO, your ears are vital as an amp builder and a musician. If you are going to be playing your new creation at loud volumes (even 5-watt amps can be painfully loud!!), wear earplugs!

RTFM! -also known as "Read The F#*%!&g Manual" Your tools and test equipment as well as some chemicals you may use all have warning labels and manuals. For your safety, the long life of the tools, AND the safety of those around you, PLEASE do this!! Also, use tools for their intended purpose!! A butter knife is NOT a good item to use to move insulated wires around in a chassis. Period.

D. Conclusion

Building and maintaining your tube amp can be a fun and a rewarding experience. AND there is no reason you can't make it a SAFE one as well for you and those around you. Please, have fun, but most of all use common sense!!!


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