Amp Safety procedures....

[amp boy]

hello all,

i am new to this forum and the idea of working on amps.
i have been doing a lot of reading over the internet on amp kits, and parts, and schematics, and so forth....
the aspect of proper safty procedures to work on amps is the one major aspect holding me back from moving towards my first build.

Can anyone suggest some working links, or information on this.
i believe this information would benefit us all.

thanks for your time and thought.
- amp boy

[vibroverbus]

Randall Aiken has great stuff check the 'Intro' section obviously, you'll see his safety doc but the others are all of interest for you as well...

http://www.aikenamps.com/TechInfo_2.htm

[Wakarusa]

There's also a wealth of information on electrical safety in the Navy NEETS training manuals.

As you read through Aiken's and other's musings it's important to keep in mind that they often assume some basic knowledge. E.g. telling you to always short electrolytic capacitors does you no good at all until you know what an electrolytic capacitor looks like -- in all its forms.

[vibroverbus]

...until you know what an electrolytic capacitor looks like -- in all its forms.

good point - and for the filter cap upgrades I do, they look like this:
http://www.dadisp.com/grafx/powsub_lg.jpg

OK OK, they look like this:
http://www.vacuumtube.com/lcr1.JPG

or this
http://www.vintage-vibe.net/Projects/Anders_Showman/Caps_New.jpg

or real old ones like this
http://www.k4qky.com/hamradio/images/old%20caps.jpg

[amp boy]

thanks for the info, any tips on discharge of cap's??
x.

[vibroverbus]

well you can do the beer swilling old timer thing and just use a screw driver to create a big spark but I strongly advise against it. i use a 10W ceramic power resistor (10K maybe?) with alligator clips soldered onto it, covered in shrink wrap. (a few nutters say don't like that either because the alligator clip insulation can fail and it gives you a false sense of security, but in my mind that's like the motorcycle riders who say "I'm safer with a helmet because it reminds me how dangerous it is".)

http://www.j2c3.com/misc/capdrainer.jpg

I hook it up across the filter caps & ground, then putter around with getting something else ready for a minute or two, and that's usually enough. it's also a big enough apparatus so that I remember it's hooked up and don't turn the amp on, although if I do, the resistance is also big enough so that it doesn't just explode or blow the fuse the second I turn the amp on too...

[pickupcentral]

thanks for the info, any tips on discharge of cap's??
x.

One of the scariest thoughts in all of newbie-dom. The discharging caps question is what kept me from a lot of fun for a long time!

One method I read about (and use) is:

Unplug the amp. Turn it on (take it off standby, too). Make sure the amp is unplugged. Did you unplug your amp from the wall? If not, unplug it. Clip a lead to the chassis and the other end clipped to pin one of a preamp tube. Do not do this with the amp plugged in. Go get a cold non-alcoholic beverage. When you come back, use your meter (set to DC millivolts) to measure ground vs. the positive end of your first filter cap. I usually start working when the amp is around 20mv or less.

-Phil

[El Caballo]

If I'm poking around in my amp, I always have a multimeter fired up, and I check the B+ voltage at the caps before touching anything else. That way I'm sure I won't get zapped. (Just connect negative to the chassis somewhere and probe with positive -- remember the one hand rule.) It's worth the peace of mind, especially when you're new to tube amps.

Some amps discharge on their own fairly quickly, especially if you leave the standby switch on (while they're turned off but still plugged into the wall). Some take a while and need help from a resistor, as vibroverbus states.

[vibroverbus]

I check the B+ voltage at the caps before touching anything else. That way I'm sure I won't get zapped.

++++1

although I'm not quite as meticulous now that I'm a bit more used to the occasional zap (i.e. stupid)

[Wakarusa]

You don't necessarily need to go get the cold beverage. The time to discharge a cap is a function of the stored voltage, capacitance of the capacitor, and the resistance it is discharged through. In most cases, it only takes milliseconds.

Sometimes big caps will "bounce". Once discharged they'll bounce back to some reduced voltage. The reason's a bit long and involved, but the upshot is that either a second round with the shorting probe or leaving a shorting device connected to a reasonable B+ point while you work are both good ideas -- provided that you always remember to remove your shorting probe before powering the circuit.

For shorting duty, I have a cheap test probe with a big enough barrel that I can fit a resistor inside the probe. I like this better than the inline 'gator clips shown above because you never stress the lead connections on the resistor. One thing that I see missing from most safety discussion here is a routine check of your gear. From time to time you should check your shorting probe to make sure it still shorts. You should also regularly test your multimeter into known sources (like a wall socket or a known DC voltage if you have one).

The "screwdriver" method -- shorting to ground with effectively no series resistance -- can reduce the working life of or destroy the capacitor. Shorting like this can exceed the current capacity of the cap and burn holes in the dielectric.

[Dion]

-- remember the one hand rule.) It's worth the peace of mind, especially when you're new to tube amps.

+++++1 The day I hired in at the power plant a guy didn't follow the one hand rule and got zapped with 400 volts/600 amps. The result still haunts a few folks I'm sure. Please use caution bro!

[vibroverbus]

...because you never stress the lead connections on the resistor.

right on waka-waka. that's exactly why I use the mega-shrink wrap method - beefy leads are soldered to the resistor, shrink wrapped with thin gauge as basic insulation, then folded back over the body and a big fat tube is shrink wrapped over the whole thing to hold it in place.

[Wakarusa]

Off topic for a moment...

Am I the only one here who actively looks for Vibroverbus' posts just to see the "rig of the day"? Pure genius :)

[vibroverbus]

Off topic for a moment...

Am I the only one here who actively looks for Vibroverbus' posts just to see the "rig of the day"? Pure genius :)

just for reference, the first and last items are always actually real gear I'm digging at the moment. stuff in the middle can come from any weirdness (don't ask about the dead cat from a few weeks ago...)

[ClinchFX]

thanks for the info, any tips on discharge of cap's??
x.

I use a 40W, 240V incandescent lamp as a discharge load.

Peter.

[amp boy]

any recommended articles or amps books, that cover safety and testing that i should read??
thanks for the discharge tips.
- amp boy.

[Wakarusa]

any recommended articles or amps books, that cover safety and testing that i should read??
thanks for the discharge tips.
- amp boy.

I always advise folks to start with the Navy Electricity & Electronics Training Series (NEETS). The USN has been using these to teach electricity to folks with not enough brains to stay out of a recruiter's office ever since dirt was rocks.

The excerpt below gives a summary of what's covered in each module. You can get 'em all at: http://www.wakarusaamp.com/library/manuals/NEETS/neets.html

There are other places on the web too, just google "NEETS".



Module 1, Introduction to Matter, Energy, and Direct Current, introduces the course with a short history of electricity and electronics and proceeds into the characteristics of matter, energy, and direct current (dc). It also describes some of the general safety precautions and first-aid procedures that should be common knowledge for a person working in the field of electricity. Related safety hints are located throughout the rest of the series, as well.

Module 2, Introduction to Alternating Current and Transformers, is an introduction to alternating current (ac) and transformers, including basic ac theory and fundamentals of electromagnetism, inductance, capacitance, impedance, and transformers.

Module 3, Introduction to Circuit Protection, Control, and Measurement, encompasses circuit breakers, fuses, and current limiters used in circuit protection, as well as the theory and use of meters as electrical measuring devices.

Module 4, Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading, presents conductor usage, insulation used as wire covering, splicing, termination of wiring, soldering, and reading electrical wiring diagrams.

Module 5, Introduction to Generators and Motors, is an introduction to generators and motors, and covers the uses of ac and dc generators and motors in the conversion of electrical and mechanical energies.

Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies, ties the first five modules together in an introduction to vacuum tubes and vacuum-tube power supplies.

Module 7, Introduction to Solid-State Devices and Power Supplies, is similar to module 6, but it is in reference to solid-state devices.

Module 8, Introduction to Amplifiers, covers amplifiers.

Module 9, Introduction to Wave-Generation and Wave-Shaping Circuits, discusses wave generation and wave-shaping circuits.

Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas, presents the characteristics of wave propagation, transmission lines, and antennas.

Module 11, Microwave Principles, explains microwave oscillators, amplifiers, and waveguides.

Module 12, Modulation Principles, discusses the principles of modulation.

Module 13, Introduction to Number Systems and Logic Circuits, presents the fundamental concepts of number systems, Boolean algebra, and logic circuits, all of which pertain to digital computers.

Module 14, Introduction to Microelectronics, covers microelectronics technology and miniature and microminiature circuit repair.

Module 15, Principles of Synchros, Servos, and Gyros, provides the basic principles, operations, functions, and applications of synchro, servo, and gyro mechanisms.

Module 16, Introduction to Test Equipment, is an introduction to some of the more commonly used test equipments and their applications.

Module 17, Radio-Frequency Communications Principles, presents the fundamentals of a radiofrequency communications system.

Module 18, Radar Principles, covers the fundamentals of a radar system.

Module 19, The Technician's Handbook, is a handy reference of commonly used general information, such as electrical and electronic formulas, color coding, and naval supply system data.

Module 20, Master Glossary, is the glossary of terms for the series.

Module 21, Test Methods and Practices, describes basic test methods and practices.

Module 22, Introduction to Digital Computers, is an introduction to digital computers.

Module 23, Magnetic Recording, is an introduction to the use and maintenance of magnetic recorders and the concepts of recording on magnetic tape and disks.

Module 24, Introduction to Fiber Optics, is an introduction to fiber optics.

[amp boy]

Thank you very much for the supporting information Wakarusa.
I'm sure this will help many of us. I have gladly already begun some of the reading. Thank you for your time.
- amp boy.