how do you short or ground a capacitor

How much electronics do you need to know before you should start messing with amps. Im thinking of buying a epiphone valve jr. and start tinkering but how much do i need to know before I jump in.

Well you should definitely know how to drain a capacitor if you are planning on messing with valve based amplifiers.

I would recommend starting with something low voltage like building an effect from a kit or something. I started out building layouts from tonepad.com and then eventually learning how to read schematics and theory and such through research, experimentation and some troubleshooting... Hell, I am still learning and experimenting... However you do NOT want to experiment with something high voltage for your first try, that could be deadly...

Here is some good info on amplifier safety... including a bit on discharging capacitors.

http://www.ax84.com/safety.html

Eh, a Valve Junior would probably be a good first project. Obviously it has to be something you're interested in and will use... if you have no interests in home made pedals or using them, then no sense spending the money and time to tinker with.

That said, as far as amps... start simple, like the valve junior. I think EL84's usually have a plate voltage between 200-300VDC which theoretically could cause injury, but in most cases the common shock at that level will be nothing more than a sharp serge up the finger or even arm. If you some how find yourself in a scenario where you cross 300VDC across your heart, then you may have problems. I've touched 430VDC in my amp and as noted, just felt a strong sharp sensation about up to my elbow. There is hardly any current within these amps.

Buy yourself a nice Fluke multimeter and some quality aligator clips before you start tinkering. Before you touch something, make sure the amp is off and unplugged (atleast until you know your way around the circuit). Check for voltage before you touch something.

To discharge a cap safely, cross a resistor from the anode to ground. In my experiences working on Marshalls, the caps don't store all that much. maybe 50V max, usually less.

They should drain off through the circuit leaving them unplugged for awhile. But its a wise safety precaution to drain them so you dont get zapped.

Its unlikely you get electricuted with the quick momentary cap discharge. A steady supply of juice is much more dangerous because it glues you to it where you cant let go. With caps its usually the reaction to the discharge that can often hurt you. You can get cut hands on chassis, busted nuckels etc as your reflexes jerk you back.

Lesson one you learn, is to only probe with one hand because there will be adjustments and troubbleshooting tests you will need learn to do with equipment running. I learned that one in TV repair a gazillion years ago with high voltage flyback transformers pumping major juice. You need to learn where the high voltage components are and insulate yourself from them. If you slip and hit something you shouldnt, you may just wind up with a paralized hand for awhile instead of a DOA.

I suggest not to try this when you don't have expert knowledge.

excellent advice

know what you're dealing with BEFORE you jump in. altho' as stated a cap will usually let you go but can also be deadly under the right circumstances, can cause heart failure.

This is where formal training comes into play. You need to be able to identify the components, the stages, the power feed wires etc before you go pokeing around. Noone jumps from a simple LRC cuircuit to a full blown amplifier and knows what they're doing.

You learn in stages starting with the most basic circuits, working in labs testing these components and verfying all the natureal laws and mathmatical formulas related to them. by the time you work up to more complex circuits, you should be able to easily identify all your components and what they do and weather that are dangerous, and you you will get some battel wounds along the way.

You will eventually need to learn to bias amps " safely" plus signal trace and other tests that can make you nervious. These should come after 6 or more months full time formal training because theres alot more to repair, building or mods than just putting a kit together.

I get a big hoot out of these guys who think they know anything by building a kit. You can get a monkey on an assembly line to pop parts on a board. Understanding what those parts do and being able to analize most of the circuit by looking at it without circuit diagrams is a good portion of it.

Its like looking under the hood of a car. You got a carb, batteries, plugs and wires, vaccume hoses altenator on the outside. You also learn the do's and dont's. around an engine using common sence, like open match near a battery or gas.

You never work under a car running or improperly rig things etc. Again there will be adjustments that are done with the engine running. If you cant handel it, do something safe for a living. Question is Do you know whats going on on the inside of the engine? How does the gas ignite and combust, how is it timed up etc etc.

It takes book study and along with hands to know what you're doing in electronics because you need to know what electricity does inside the individual components to achieve the specific effects. Even then you come across some cockeyed arrangements in amps where you need to look up and see why they did things that way.

So you can build a kit and learn a few tidbits here and there on the net, but you arent going to develop much more than a hack knowlege of electronics and can be a danger to yourself and others by not knowing whats safe or not. If you want to work in the industry it really does require formally learning what your doing.

I did most of my stupid stuff as a kid without the training. lockilu I didnt burn down the house or electricute myself but came close a few times.

Theres a Adult ed. class at a technical school classes start a $300 for like a 10 2hour lessons

I don't think you need to take courses unless you're looking to do this professionally, or have a strong desire for instructed learning. You can learn a lot of basic electrical safety from many sources... the internet being most convenient. Once you know how to work safe then you're free to tinker. To tinker doesn't require you to be an expert in electronics or guitar amp circuitry. You can read about tips and suggested mods and so on, and try them out for yourself. You can deviate from those mods to try your own or better them (etc) once you have a basic understanding. You can learn a lot from hands on experience, even when it's unsuccessful.

I personally have a bachelors degree in electrical engineering, and am currently an industrial electrical engineer for one of the biggest companies in the world. I am not an expert in electronics or amplifiers but it's a hobby and I don't feel i need to be an expect to replace and bias tubes, to make simple repairs to expired components, to play with component values (within reason) and see how they sound.

If it's just going to be a hobby for you, you shouldn't have to worry about fancy or extensive training, unless you want that and will pay for that. Ideally, just do some homework, learn some basics, buy some quality tools, tinker with something that interests you, and be prepared to invest a lot of time and brain power (and probably money too, lol).

Maybe I'm just another hack, but my main point is don't feel extremely overwhelmed. A lot of people have learned about electricty, electronics, and guitar amps. It's not a "high tech" subject. There is a lot of knowledge that can be gained at no cost my doing some simple research and small scale experimentation. Asking questions here, as you had, it a good start.

Best of luck!

I have used a 100 ohm resistor attached to a wire for discharging. When I used to do component repair on computer terminals, I would sometimes need to discharge the CRT. A few minutes later, I would reach over the tube and it would shock me. I had to discharge them multiple times.

CRT shocks are the nastiest bites ever. The way I'd do them is to use plyers with rubber coated handels, disconnect the high voltage wire from the tube and ground the high voltage wire.