Valves Book
 

"Andy Evans" wrote in message
...
don't hit the 500VDC supply with a spanner while hanging onto the metal
rack
with the other hand.

Too right. start experimenting on 300v HT lines. Not that they can't do
you in,
but you can survive.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

You should also respect large heater DC caps also
To quote from Morgan Jones, p236

"A 10 00µF is capable of delivering a very high current into a low
resistance., and wedding ring across the capacitor will discharge it
perfectly. The explosive arc that will be struck at the instant of
discharge will cause the ring to vaporize, resulting in flying molten
metal. Do *not* wear jewellery when working on low voltages"

But, don't let us put you off. Just beware and be careful.
Enjoy!

Iain

Valves Book
 

Don Pearce wrote:


Just one more thing - don't hit the 500VDC supply with a spanner while
hanging onto the metal rack with the other hand. You travel a long
way, and you don't find the spanner again.

d
Pearce Consulting
http://www.pearce.uk.com

I agree with all that, and to add a bit more. Gloves may help the nerves
for the first amp, but eventually you find that they are just a pain.
Better to learn proper safety rules from the start, if you start to
think its ok to touch 600v with gloves on, you may forget one day to put

them on. Its like any other risky activity, the trick, is to learn to
think about what you are doing, before you start to do it, and think
where both hands are, and any other part of the body that may be in
contact with a earth.

You may find people who have done this for a long time, look as if they
are very casual about what they are doing, they are not, its just that
the habit of thinking what you are doing and being aware of whats going
on is so ingrained that they do it almost without thinking.

Also don't fall into the "Well, this wire is only connected to 6.3v, so
its quite safe, and nowhere neat the HT+". That may be how it should be,

but things don't always go to plan ;-)

--
Nick

"Life has surface noise" - John Peel 1939-2004

Valves Book
 

I'd add the injunction NEVER to work on equipment late at night when tired or
when drunk. These are the times when you may feel inclined to 'have a go' or
listen to a project. Resist. Wait until you are bright and fresh.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

Valves Book
 

In article , Andy Evans
wrote:
The obvious epic here would Langford Smith.

Epic's the word - to a beginner it's about as readable as Homer's
Oddyssey (in the original Greek...)

That's why I send "end up" when mentioning it. :-)

I still dip into it and find things that I didn't know were there, or had
understood previously.

Above said, once you have the basics of electronics, Langford Smith should
be quite readable. But some patience is required as it contains so much
info, and requires some thought.

e.g. if someone has worked their way through the "Scots Guide", and gained
some practical experience, I'd hope they could then easily follow Langford
Smith.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Valves Book
 

In article , Andy Evans
wrote:
I'd add the injunction NEVER to work on equipment late at night when
tired or when drunk. These are the times when you may feel inclined to
'have a go' or listen to a project. Resist. Wait until you are bright
and fresh.

I'd add: Never work on a Friday afternoon. You will probably write off all
the progress you've made earlier in the week. Remember to keep Poets Day
Holy. ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Valves Book
 

Jim Lesurf wrote:
In article , Don Pearce
wrote:



Just one thing to remember. When working on live valve circuits, keep
one hand in the pocket at all times.


You beat me to that. :-)

I'd add: make sure the mains switch on the wall is within easy reach. There
will be times when you wish to switch off the unit in front of you with
minimal delay. :-)

Also, "do not poke components with a pencil".


Crepe-soled shoes are a help, too. (I know, that's two things). I found
all that out the hard way in my early days of design.


One of my ex-colleagues used to work on HV discharge lasers 'live' whilst
wearing rubber boots. Mind you, he was a bit crazy. Doubt the
health-and-safety people would let you do it now.

I have always been much more slow-and-cowardly. If kit has mains, or above
about 50Vdc I am inclined to keep shutting everything down when I want to
move probes about, etc. Slower. But you get time to think about what comes
next, and may live longer to do more thinking. :-) Also checks out that
the kit can be turned on and off a lot without problems.

I also tend to prefer bench supplies when developing or testing an amp, and
only connect to the working PSU when doing more protracted tests. Bench
supplies give more safety options, and can also be useful for checking
other effects, etc.

Hence my other advice tends to be "pause and think again, and try to work
out what devious ways the kit in front of your has just devised to try and
kill you." This is also what tea breaks are for.


Just one more thing - don't hit the 500VDC supply with a spanner while
hanging onto the metal rack with the other hand. You travel a long way,
and you don't find the spanner again.


My personal estimate is that about 2kV equals about one rotation of the
human body and you bowl over backwards (if lucky). This is roughly what I
did one day courtesy of someone else rewiring a klystron without telling
me.

Slainte,

Jim


Many thanks all - I appreciate your words of caution. I have no
intention of fiddling with the Beard amp I've got - that's going to a
professional, what with its 2kV voltages and all!

Given my known ****wittery I'm going to go verrrry slow.

:-)

Rob

Valves Book
 

On Sat, 11 Dec 2004 16:49:19 +0000 (GMT), Jim Lesurf
wrote:

In article , Don Pearce
wrote:

Just one more thing - don't hit the 500VDC supply with a spanner while
hanging onto the metal rack with the other hand. You travel a long way,
and you don't find the spanner again.

My personal estimate is that about 2kV equals about one rotation of the
human body and you bowl over backwards (if lucky). This is roughly what I
did one day courtesy of someone else rewiring a klystron without telling
me.

After we'd checked that he wasn't seriously hurt, one the funniest
things I ever saw was in my days at Marconi Space and Defence. One of
the guys was kneeling into the back of a rack cabinet, working on a
200 volt DC PSU which had about 30,000uF of reservoir capacitance on
it. He accidentally touched one of the cap terminals, which threw him
backwards. His head hit the top of the cabinet doorway, which threw
him forward so that he hit the cap array, which threw him back into
the doorframe, which threw him......

He must have completed about five oscillations before he eventually
missed the doorframe and flew across the lab floor! After the intial
rush to check that he was basically OK, we absolutely howled.... :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Valves Book
 

On Sat, 11 Dec 2004 21:02:38 +0200, "Iain M Churches"
wrote:


"Andy Evans" wrote in message
...
don't hit the 500VDC supply with a spanner while hanging onto the metal
rack
with the other hand.

Too right. start experimenting on 300v HT lines. Not that they can't do
you in,
but you can survive.

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.

You should also respect large heater DC caps also
To quote from Morgan Jones, p236

"A 10 00µF is capable of delivering a very high current into a low
resistance., and wedding ring across the capacitor will discharge it
perfectly. The explosive arc that will be struck at the instant of
discharge will cause the ring to vaporize, resulting in flying molten
metal. Do *not* wear jewellery when working on low voltages"

Agreed. Even 12 volts can be very nasty. I once shorted the starter
solenoid of my car with my watch bracelet, which went to dull red in
about a second! I can recommend Omega Seamasters, they will survive
being ripped off a wrist and thrown across the street..........
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Valves Book
 

"Stewart Pinkerton" wrote


Agreed. Even 12 volts can be very nasty. I once shorted the starter
solenoid of my car with my watch bracelet, which went to dull red in
about a second! I can recommend Omega Seamasters, they will survive
being ripped off a wrist and thrown across the street..........


Hmmm, I think I gave my brother one of those about ten years ago - black
face, white hands, looked like a mini-submariner with an RRP of about a
thousand?

I have *never* seen him wearing it. Everytime I see him now, the urge to
mention it is growing stronger (like 'if you don't want it, I'll have the
bloody thing back!!') - not helped by all this 'genuine replica' spam I get
on a daily basis....

Valves Book
 

Beard amp I've got - that's going to a
professional, what with its 2kV voltages and all!


2Kv on a Beard amp????????? Where?

=== Andy Evans ===
Visit our Website:- http://www.artsandmedia.com
Audio, music and health pages and interesting links.