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DrDeville 13th March 2004 08:42 PM

Safety Practices, General and Ultra-High Voltage
I want to live. :hbeat:

In the interest of safety, I would like to collect whatever safety tips and practices this forum kindly and experienced members will share, so that all may benefit. :grouphug:

First, some warnings and disclaimers:
  • Any voltage can be deadly. :hot: :RIP:
  • Amplifiers are dangerous--each person (me included) is responsible for deciding if they are willing to risk their life, and for ensuring that whatever information they receive is correct
  • This forum and its members accept no responsibility for any death, injury or property damage that result from any of these suggestions--your safety is your own responsibility.

And please note that I have *no* amplifier hardware on hand, and will not for a while. This is a discussion only, and I will only be talking about doing stupid things, not actually doing them.

Okay, with that out of the way, I would like any tube equipment electrical safety advice you care to share, both in general, and for what I will classify (for the purposes of this discussion) as UltraHighVoltage--1000V to 1500V.

I'll start with what I think I know, and you can add more or correct me if I am wrong.

I can think of two basic rules of thumb--
  • Make sure any charge-storing devices remain discharged while working on the equipment
  • Avoid creating a circuit which would pass current through the heart.

From those rules of thumb, I can think of these specific practices:
[list=1][*]Put a drain load across all significant charge-storage devices (e.g. B+), and leave them there for the duration of your work--some devices can redevelop voltage if left unloaded.[*]Verify that all charge-storing devices are discharged before starting work.[*]Always work with only one hand--keep the other hand in your pocket.[*]Use hook probe for secure connections and to avoid shorts.[*]Wear rubber gloves and rubber soled shoes--no bare feet or socks.[*]Make sure your design has the chassis safety grounded--connected to the ground wire of the power plug.[/list=1]

Okay, what do you think about these practices, and what can you add?

One member spoke of a "bench isolating transformer". What is that, what does it do, and how is it installed/used?

Also, what extra design and usage practices apply to UltraHighVoltage (1000V to 1500V) electronics? I'm thinking about things like component choices, test procedures (standard DMMs are only rated to 600V), design practices (danger of arcing), etc.

Thanks for your attention and advice. Although I hope for courtesy, I'd rather be flamed figuratively than literally. :hot: ;)


George Ferguson

Netlist 13th March 2004 08:57 PM

Nice thoughts.
I've seen these safety issues pop up on a very regular basis here on the forums.
Maybe it's time to compress them in a new wiki page.
This would make a nice reference for all of us. ;)

SY 13th March 2004 08:59 PM

Thanks for starting this thread. If it develops well, we'll make it permanent.

Just some general comments that I've made before:

Reflexes, habits, and instincts appropriate to low level low voltage stuff can be deadly. At a previous company, I hired an exceptionally bright young engineer with lots of practical knowledge to do design and prototyping work on some computer peripherals. He took it in his head one day to fix one of the ovens that we used for curing resistors; while probing around with a voltmeter, all interlocks cleverly defeated, he managed to accidently brush against one of the 460V rails. He had probably done that sort of thing a thousand times before with the microcontroller and logic circuits he breadboarded, and though he certainly understood the hazards on an intellectual level, it wasn't reflexive. In the bloodhound heat of concentrating on the quarry of the oven failure, he got careless.

He is no longer a bright young engineer.

When you decide to work on high voltage circuits, spend time around experienced guys. Never work alone. For ultrahigh voltage stuff (high power supplies at 1kV and beyond), all the rules are different and you would be INSANE to the level of suicidal to tackle such a thing without the direct supervision of an experienced guy who wishes you no harm.

Too paranoid is much preferable to not paranoid enough.

DrDeville 13th March 2004 09:12 PM

Sy Said:

When you decide to work on high voltage circuits, spend time around experienced guys.
Sounds like sage advice. Can you tell us some ways, particularly online, to locate such folks?

I've found the National Association for Amateur Radio at and am contacting them.

Where else should I look?


George Ferguson

SHiFTY 13th March 2004 09:28 PM

A couple of things I have learned, in addition to those already mentioned:

:att'n: Make sure the unit is turned off at the wall, and preferably unplugged before working on it.
:att'n: If you have to make live measurements, use crocodile clip-leads on your DMM so you can turn on, measure the voltage, turn off.
:att'n: Use the proper insulated top cap when required.
:att'n: Don't use a screwdriver to short a charged capacitor!

djmiddelkoop 13th March 2004 10:25 PM

Here are some more:

Use a High Voltage probe to make measurements.

Use High Voltage parts, like resistors have a max voltage to, check the specs.

Use isolation where possible to prevent unwanted flash overs.

Use your mind !

Layberinthius 13th March 2004 10:56 PM


Use High Voltage parts, like resistors have a max voltage to, check the specs.
Yeah "Too" all components including wire insulation have a maximum allowable voltage and indeed resitors.

If you don't know how to figure out a resistor's voltage rating, ask for more help! you are no where near ready...

If you were using 250volt 10amp rated wiring in an amplifier that was going to have a 1000v B+ you could not use the wire and not expect electricity to shoot out of the side through the insulation and onto something nearby, like a finger or more commonly a chassis.

Also, don't ever service a TV set, don't even open one up as the chassis in two-conductor televisions are live and will kill you as they are just as if you stuck a fork into the power point, only there is much more contact area. Of course, it may be something simple and you want to see your fav programme, pay a qualified TECH to do it!! Don't take it to your friend's grandfather or your father!

Do you think a retired welfare guy has enough cash to afford all the equipment needed to fully and properly service your TV/VCR?

Believe me, you'll be doing them a favour! especially with all the new TV's out, plastic here plastic there shotty cheap components everywhere... digital this digital that. mongrels...

And never service old radio/amplifier equipment using the same wire which was in there for 50 years, the insulation /will/ fall apart
someday or even worse catch fire from excessive heat.

Always replace electrolyctic capacitors in equipment 10-15+ years old, just because an old set is 'working' doesn't mean it's going to be working for another month or 6. THESE EXPLODE PEOPLE!

Same goes with the old resistors, they are a very high fire risk especially if old-man sprays WD40 over the pots and fires it up straigt afterwoods :P Generally this is okay if you leave it for a few seconds, as it cleans the dirt and corrosion off the pot contact.

However some variants may have a low-evaporative rate and a high flammability, WD40 dries out eventually..

Generally on the output transformers the secondary voltage is too low to become dangerous, however with high impedance taps like 50-150-300 ohm taps for PA work the voltage is stepped up to god-only-knows hundreds of volts, this will give you a nasty tingle or start a fire with poor quality speaker cable!

Aswell, If a tube has a WHITE 'powder' inside it means that the tube has lost it's vacuum!! completely!
if the powder is silver or black it is FINE black actually means it's
got a better vacuum than a silver one so I recommend you don't
return it just because the powder looks 'stressed' or 'burnt'.

You're more than welcome to return it due to any concern, I'm not stopping you. Like a lop-sided tube, wriggly pin, looks weird inside, when you shake it you can hear a ting or ping, etc.

Just my $5, if anyone would like to comment, just notify a moderator or send me an email and I will modify this posting for the next 30mins, I don't get angry if I've been fed bad information at the person who notified me of that fact.

Anyone at any time can place a notification to the moderator about a specific post just by clicking "Report" on the bottom righthand side of the post-box..


SY 14th March 2004 12:12 AM


Originally posted by DrDeville
Sy Said:

Can you tell us some ways, particularly online, to locate such folks?

I've found the National Association for Amateur Radio at and am contacting them.

Where else should I look?


George Ferguson

Hams are a great start. Look for geezers like me.

Also older TV repairmen; they'll be tough to locate on line, but a wander through your neighborhood or your phone book might be productive. An offer of some free labor will go a long way toward securing lessons- that's how I got started.

DrDeville 14th March 2004 02:51 AM

djmiddelkoop said:

Use isolation where possible to prevent unwanted flash overs.
Hey DJ,
Nice lederhosen! ;)
Could you explain isolation, in theory, and maybe give an example? If not, I'll try to track it down. :magnify:

Thanks all, for the comments--please keep them coming. At some point, I will summarize them, for further comment.


George Ferguson

djmiddelkoop 15th March 2004 01:35 AM

George, some examples:

high voltage wire
RTV aka Silicone rubber ( if possible use the acid free)
PTFE tape, tube or sheets


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