Tips for working with high voltage?

[Scott674]

I've been looking at these pedals that use Tubes and Transformers and whatnot in them, and they look quite interesting.  I wouldn't mind building one of these myself (Sooner or later, I'd even like to build my own tube amp), but I'm nervous about these tubes and transformers...   Is there a recommended resource or does anyone have any tips for working with these high voltage items?  How they work, how to discharge them, insulate them, etc...  Thanks!

[mountainking]

The fact that you have these questions means that you are a long ways off from working with high voltage circuits. You will never learn how to safely work with high voltage by just reading about it, you need someone with years of experience to teach you and walk you through it so I suggest taking a class.

Alan

[John Lyons]

If you are careful and read about it you will be fine. Don't be scared of HV, just be smart about it and take your time.

Some tips.
Always discharge the caps of an unknown amp before poking around.
Measure the voltage of any HV caps before you start working on the amp.
Make a discharging tool with a 2 foot length of wire, a one watt 100K resistor on one side and and an alligator clip on the other.
Insulate the resistor so you can use it as a probe.
Clip the wire to the chassis or anything directly grounded and touch the resistor tip to the plate or any HV points and the voltage will dissipate.

Keep one hand in your pocket while working on a live amp. This prevents you from getting shocked through your heart.
Use a chopstick or any electrically non conductive poker to work in an amp.

Read as much as you can and get to know what everything looks like inside an amp.

Some place you can go to learn are.
AX84.com, EL34.com
There are many resources there as well. Use the search engines there to find out about reading material etc.

You will know when you are ready. There is no substitute for experience but as long as you read like mad you will at least know what to expect and be familiar with what's going on inside.

John

[mojotron]

If you are careful and read about it you will be fine. Don't be scared of HV, just be smart about it and take your time.

Some tips.
Always discharge the caps of an unknown amp before poking around.
Measure the voltage of any HV caps before you start working on the amp.
Make a discharging tool with a 2 foot length of wire, a one watt 100K resistor on one side and and an alligator clip on the other.
Insulate the resistor so you can use it as a probe.
Clip the wire to the chassis or anything directly grounded and touch the resistor tip to the plate or any HV points and the voltage will dissipate.

Keep one hand in your pocket while working on a live amp. This prevents you from getting shocked through your heart.
Use a chopstick or any electrically non conductive poker to work in an amp.

Read as much as you can and get to know what everything looks like inside an amp.
...

All good points...
I would add that I use a computer power strip to turn power on/off between moving alegator clips to where I want to make voltage checks, I don't use probe tips too much as one slip can cause a lot of arcing and things getting nasty.

Also, from personal experience , when you start to feel comfortable working with a live high-voltage start to be more careful. Being comfortable is OK, but you just don't want to get careless.

Any danger with electrical gear can be mitigated with good safety awareness.

[gez]

I have really poor concentration these days so I don't like to go poking around in high voltage stuff.  Although I've always carried out basic repairs on my amps, I never had to do serious repairs until a few years ago (by serious, I mean my amp had to be up and running while I was debugging it).  At the time, I read the stuff at GEOFEX (thanks RG, it was a big help) and a few other sites.  It gave me the courage to tackle the job myself and all was fine.  Probably paranoia on my part, but I also wore rubber gloves while doing any 'live' testing.  Anyway, it all worked out fine (I'm still alive), just do plenty of reading first and visualise what you have to do before you do it.

[petemoore]

  I like to make the actual open amp work to occur 'later'...
  After lots of reading, gathering diagrams/schematics/etc. drawing up on paper maybe some stuff, all the research and ferreting out info's.
  Just drew a few transformer diagrams, color coded wiring notations and #'d lugs, had to send on back [wrong taps !!], so just now it is a very good thing I decided to have both irons pulled w/AC'd primaries, measuring all the secondaries...
  So I find it is best to wait until there is no rush whatsoever and I feel like I've got everything I need all satisfactorily sorted out and hopefully notated on paper so I can remember all the details I worked to understand as best I can.
  Be certain the drain resistor line is very securely insulated, don't touch the uninsulate parts.
  Getting used to the drain resistor procedure...EVERY time, I put it on a yellow wire which gets hooked right to the ON switch, a reminder method which must include the procedure: *unplug of AC / connect drain resistor / Watch B+ voltage drop to safe level like 0.0vdc With DMM*.
  Find a time when you won't be called away from concentrating, if you are called away, repeat and verify the drain procedure list.
  I put tape on the drain resistor, though I never have forgotten to disconnect it [Daft:  lately] the tape provides a smoke warning that the drain R is getting very hot.
 

[remmelt]

Just like with a gun: unless you have personally checked it this moment, assume the gun is loaded. Same goes for the caps: assume they are loaded with HV. Good point above: make it a routine to check power off/unplug amp/drain voltage/check voltage. Each time. Don't skip one step or one time, because you'll get zapped (mine was from the 220 mains. BAM!) I would suggest you leave the drain resistor in the amp when you're not working on it or playing it, so you have a visual confirmation about the state of the caps. And still check with a DMM.

As for experience, I assume you've built a couple of effects and have read up about tubes and how they work. I downloaded copies of some tube amp books and read those, trying to really understand what was going on. Partly for safety reasons, partly for a deeper understanding of the inner workings. This seems to greatly improve the chances of something working on the first go for me.

Then I bought a kit from tubeampdoctor.com. They're not the cheapest but the kits are of great quality. No regrets there. A kit because I wanted to make sure all parts were of the right value/wattage/etc.

The result: a Fender Champ replica!

[frankclarke]

http://www.geofex.com/ tube amp FAQ.
Very much like firearms safety, you have to drain the caps and measure every time you come back to it and after you power it down.

[DougH]

One thing that helps with safety are good habits. This means establishing a routine and following it exactly, every time. Don't let yourself lapse into thinking the caps are bled, even if you have a bleeder resistor. Check them every time before you stick your hands in the amp. Always check to make sure the AC power is unplugged as well. Always keep one hand in your pocket during live testing, etc. Don't be afraid of using a meter probe. Used the same way you would with a 9v circuit, it will not arc, although you may hear a "pop" through the speaker when touching sensitive signal points in the circuit. Keeping it vertical will help you avoid shorting it on something and causing arcing. (Always handle the insulated part of the probe, of course.) And so on...

It's not difficult to stay safe when working on an amp. Just be aware of what you are doing at all times.

[PerroGrande]

Another "nice to have" when working on tube circuits is a variac / autotransformer.  Not only does this provide some degree of isolation, but it allows you to bring the voltage up slowly -- very useful if you've got an amp that wants to blow fuses...

All of the other caveats that others shared certainly apply.  Like anything else involving "force" -- respect and understand, but don't fear.   

If you want to get into tube technology without the worries of the higher potentials, you could explore some of the low voltage options as a start.  You could get familiar with the characteristics of tube design and building without the large B+ voltages looming in the background.  Might be a useful intermediary step to get you on tour way.

[petemoore]

  A jig to hold the amp in a 'work' position which prevents the tubes from becoming support members or broken. The right sized droor is what I use, though it is a simple matter to make a wood amp mounting jig, U shaped so it supports from the chassis, generally that'd be tubes down position.
  A tall/long, close-in, adjustable high intensity quartz light with certainly helps with my lighting needs.
  Clean bench, parts dishes or containers.