There used to be a question on the Navy ET exam that goes like this:

What is worse when working on a ships service panel--to put your hand on a
120V main, or a 440V main?

The answer is 120V main. 440V causes the body to reflexively fly off the
offending spot. A 120v Main can freeze the hand to the main, and cause
electrocution.

I get zapped by 400-800v about once a month (Yeah I know--stupid, stupid,
stupid). Since all my bench power is isolated--it just gives me that needed
wake up call. After a while, it doesn't even hurt that much.

The most fun (If I can use that word) I had with a shock was in 1969 at the
U of Indiana. I was studing Physics and my amp quit working--I needed music
to keep going. So I thought I'd take it apart and see what was wrong--of
course leaving it live since I didn't have any test equipment in the dorm
room. Well as I was poking around there was an enormous blue flash between
a couple of components and all the lights in the dorm went out at the same
instant. I thought, great, I blew the fuse--and how am I going to get it
replaced at 2AM in the morning. Then I looked out the window and noticed
that all the lights on the Campus were out. That seemed a little
supicisious. Turns out, a drunk driver had plowed through the city
substation at a high speed--at exactly the same instant as I shorted out
something in the amp. Since everyone was studying for finals at the
time--they all blamed me.

When I was young ( in my teens ) and working on tube amps, I was less
careful. I get shocked
quite frequently. I can tell from the shock if I have touched the 240V ac or
the HT because the feeling is
different. If you don't believe me, go try it yourself ( at your own
risk ).. The worst shock I ever had is from a B/W
television ( fortunitely it was a B/W set - lower EHT ). My finger was about
half an inch from the EHT connector
and the spark jump out at my finger. It was not just a shock, it was
actually very pinful and last quite a while.

Stevey wrote:
When I was young ( in my teens ) and working on tube amps, I was less
careful. I get shocked
quite frequently. I can tell from the shock if I have touched the 240V ac or
the HT because the feeling is
different. If you don't believe me, go try it yourself ( at your own
risk ).. The worst shock I ever had is from a B/W
television ( fortunitely it was a B/W set - lower EHT ). My finger was about
half an inch from the EHT connector
and the spark jump out at my finger. It was not just a shock, it was
actually very pinful and last quite a while.



My most memorable were the arc that jumped from an old Tube scope to my
thumb..I had it on it's side,pluggd in on the kitchen counter,trying to
find out why one channel wouldn't work correctly...
*ZAP*
An arc jumped a good 2-3 inches from the focus/brightness pot to my
thumb. Left a nice black crater in the end of my thumb,and it *hurt
alot*,like it arced to a nerve ending or something.
Smelled like burnt flesh too. (Eeewww.)

The other was my laser power supply..
Fiddling with it,unplug it..
Check the ballast resistor,make sure it's not too hot-it's okay...and..
*WHAMMO*
-It felt like a baseball bat across the chest.-
I immediatly jumped up and checked for my pulse.
I almost needed to change my pants after that one.Scared the holy
bejesus out of me.

Yes,It's a concern.
And Yes,you need to be damn careful.

"Ptaylor" wrote in message
...

Yes,It's a concern.
And Yes,you need to be damn careful.

A veteran amp builder with whom I sometimes work, was a
radar technician in the Army. On his workshop wall he has a
thick glove with a huge hole burned into the top of the index finger.
There is a large charred area surrounding the hole.

It happened years ago, but it a constant reminder.

As mentioned elsewhere, I always have a discharge box across
the reservoir cap of an amp when I am tinkering., and when
building something new, I use a bench psu, and no external
electrolytics so that when the psu output if "off" there is no
DC present.

Safety is a primary concern. Any tips would
be of interest.

Iain

I finally made a bench HT power supply using regulator tubes and taps for
most voltages that I would use.

THe most important part of this supply was the auto shorting switch the
dumpes the caps when I turned off the supply to work on the circuit in
question.

If there is any interest I can give the basic design of the PS. Very cheap
to build and gives filtered 100,150,205,225,250,310 VDC, 480 AC, and
unfiltered 380DC. Allows shunt or series regulation. Has 2.5VDC, 5.0VDC,
6.3VDC taps as well. Total cost $10 from surplus house parts. Max of 40
ma regulated.

WHen I need high current I use my Lamba 400VDC variable supply that one of
the RATS was kind enough to sell me for $50.

"Iain M Churches" wrote in message
...

"Ptaylor" wrote in message
...

Yes,It's a concern.
And Yes,you need to be damn careful.

A veteran amp builder with whom I sometimes work, was a
radar technician in the Army. On his workshop wall he has a
thick glove with a huge hole burned into the top of the index finger.
There is a large charred area surrounding the hole.

It happened years ago, but it a constant reminder.

As mentioned elsewhere, I always have a discharge box across
the reservoir cap of an amp when I am tinkering., and when
building something new, I use a bench psu, and no external
electrolytics so that when the psu output if "off" there is no
DC present.

Safety is a primary concern. Any tips would
be of interest.

Iain

tubesforall wrote:

I finally made a bench HT power supply using regulator tubes and taps for
most voltages that I would use.

THe most important part of this supply was the auto shorting switch the
dumpes the caps when I turned off the supply to work on the circuit in
question.

If there is any interest I can give the basic design of the PS. Very cheap
to build and gives filtered 100,150,205,225,250,310 VDC,

Looks like a row of VR tubes!! Cheers, JLS

480 AC, and
unfiltered 380DC. Allows shunt or series regulation. Has 2.5VDC, 5.0VDC,
6.3VDC taps as well. Total cost $10 from surplus house parts. Max of 40
ma regulated.

WHen I need high current I use my Lamba 400VDC variable supply that one of
the RATS was kind enough to sell me for $50.

"Iain M Churches" wrote in message
...

"Ptaylor" wrote in message
...

Yes,It's a concern.
And Yes,you need to be damn careful.

A veteran amp builder with whom I sometimes work, was a
radar technician in the Army. On his workshop wall he has a
thick glove with a huge hole burned into the top of the index finger.
There is a large charred area surrounding the hole.

It happened years ago, but it a constant reminder.

As mentioned elsewhere, I always have a discharge box across
the reservoir cap of an amp when I am tinkering., and when
building something new, I use a bench psu, and no external
electrolytics so that when the psu output if "off" there is no
DC present.

Safety is a primary concern. Any tips would
be of interest.

Iain

"John Stewart" wrote in message
...


tubesforall wrote:

I finally made a bench HT power supply using regulator tubes and taps for
most voltages that I would use.

THe most important part of this supply was the auto shorting switch the
dumpes the caps when I turned off the supply to work on the circuit in
question.


Yes, my 600V 0.5A Solartron valve bench psu does just that.

Iain

Iain M Churches wrote:
"Ptaylor" wrote in message
...


Yes,It's a concern.
And Yes,you need to be damn careful.


A veteran amp builder with whom I sometimes work, was a
radar technician in the Army. On his workshop wall he has a
thick glove with a huge hole burned into the top of the index finger.
There is a large charred area surrounding the hole.
It happened years ago, but it a constant reminder.


Eek!

As mentioned elsewhere, I always have a discharge box across
the reservoir cap of an amp when I am tinkering.,

That is a good tip.
Thats something I always tell my friends/newcomers to tubes.
-Before- you put your fingers in an amp,clip a resistor ascross the
B+/caps,and leave it there for a few minutes while you gather your
tools,etc. and just let the caps discharge for a bit.

And then,leave it there untill you're done working on the amp -
capacitors can have a bit of a "memory effect" and -RECHARGE THEMSELVES-
I've measured it with my DMM more than once.
Leave the resistor inplace untill you are finished,BUT don't forget to
remove it before you power up the amp again! A smoking resistor and/or
fuses blowing can be frustrating. ;-)

I always put "bleeder resistors" inside the amps I build,usually
something like 220-470K 1/2-1W depending on the application.
Just something to drain the capacitors in a few minutes,after I power it
off,and unplug it.. By the time I get it apart and may be in danger,the
caps *should* already be discharged.However..Resistors CAN sometimes go
open,which means the caps would still be charged,and you might get "bit".

*The number one rule.. -*carefully* TEST IT with your DMM before you
touch it.*

And use your well insulated resistor-thingie to discharge the caps if
they Are charged.

Seriously,I've gotten "bit" bad a couple times..I used to be sligtly
careless with HV,fortunatly i'm still here.It only takes one "baseball
bat" incident to make you snap out of it real freakin quick like.(or to
snuff you out,for good.) I'm damn careful now -and want whomever may
happen to read this,to be damn careful too. Read up online,gather the
needed tools,and make some discharging resistor-rod-thingers,and
whatever. Don't risk your life.

DON'T F*%^ with High Voltage.Respect it. It only takes ONCE to KILL.


and when
building something new, I use a bench psu, and no external
electrolytics so that when the psu output if "off" there is no
DC present.

Safety is a primary concern. Any tips would
be of interest.

Iain

tubesforall wrote:

There used to be a question on the Navy ET exam that goes like this:

What is worse when working on a ships service panel--to put your hand on a
120V main, or a 440V main?

The answer is 120V main. 440V causes the body to reflexively fly off the
offending spot. A 120v Main can freeze the hand to the main, and cause
electrocution.

I get zapped by 400-800v about once a month (Yeah I know--stupid, stupid,
stupid). Since all my bench power is isolated--it just gives me that needed
wake up call. After a while, it doesn't even hurt that much.


Never work barefoot. (plastic or rubber floor mat, not a bad idea)

Take your time, never hurry.

One hand in your pocket or behind your back when probing a HV B+ area.

Don't rest your hand or arm on the chassis, either one.
(if you need something to lean on, pile up some books or a plastic item)

If ur not in the right position, MOVE something!

Don't have a bare metal bench or a bench with bare or painted metal
sides or top (it thinks it's ground)

Discharge the caps.
Measure them.
Short them. Or use a low R resistor which will get hot and stink when
the power is still on. (it's disposable, eh?)

Beware of High Voltages, they jump.
Beware of RF, it jumps and makes nasty holes in you.

On really seriously high voltage/power stuff use a *shorting stick*,
kill the mains, kill the power switch. Double check, Triple check. Test
with a meter before sticking hands any where near anything.

--- If yr getting shocks once a year or more, that's too much, ur doing
something very wrong. You may well wind up dead without notice. ---

ELECTRICITY AS FOUND IN TUBE GEAR IS DANGEROUS!!

*USE CAUTION*

_-_-bear

"BEAR" wrote in message
...

Never work barefoot. (plastic or rubber floor mat, not a bad idea)

Take your time, never hurry.

One hand in your pocket or behind your back when probing a HV B+ area.

Don't rest your hand or arm on the chassis, either one.
(if you need something to lean on, pile up some books or a plastic item)

If ur not in the right position, MOVE something!

Don't have a bare metal bench or a bench with bare or painted metal sides
or top (it thinks it's ground)

Discharge the caps.
Measure them.
Short them. Or use a low R resistor which will get hot and stink when the
power is still on. (it's disposable, eh?)

Beware of High Voltages, they jump.
Beware of RF, it jumps and makes nasty holes in you.

On really seriously high voltage/power stuff use a *shorting stick*, kill
the mains, kill the power switch. Double check, Triple check. Test with a
meter before sticking hands any where near anything.

--- If yr getting shocks once a year or more, that's too much, ur doing
something very wrong. You may well wind up dead without notice. ---

ELECTRICITY AS FOUND IN TUBE GEAR IS DANGEROUS!!

*USE CAUTION*

Good advice to all.

Perhaps we should add:

Only work for shortish periods - don't use alcohol.

Be cautious of *all* electrolytics,even those use in heater
circuits. A quote from Morgan Jones with regard to the design
of LT supplies:

"A 10 000µF capacitor is capable if delivering a very high
current into a low resistance, and a wedding ring across the
capacitor will discharge it perfectly. The explosive arc that will
be struck at the instant of discharge will vaporize some metal
resulting in flying molten metal. Do not wear jewellery even
when working on low voltages"


Iain