Safety Practices, General and Ultra-High Voltage - Page 6 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 9th December 2004, 07:18 AM   #51
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Default Beware of insulation breakdown

Mains Voltage Differences

Ensure that the component you plan to use is rated for the correct mains voltage. The mains voltage in North America and Japan is about half of that in the UK, Europe and many other regions (including SE Asia, Australia and New Zealand). Switches, power sockets, etc. sourced from Japan or North America can be unsafe if used in other countries.

Using Mains-Rated Devices in a B+ Circuit

I experienced an alarming breakdown of insulation, recently, when I used a panel-mounted barrel-type fuseholder to protect the B+ of my amp's power supply against overload. The max. voltage rating was not marked on the fuseholder but I'm now guessing it must be 250v or less. The result of using it in a 400v circuit was that a carbon track got burned through the plastic body, from the mounting collar of the fuseholder to the inner thread into which the fuseholder cap is screwed when mounting the fuse. There was a loud crackling sound and spectacular sparks could be seen, both above and below the chassis. There was also a noxious stink of burning plastic.

Strangely, I couldn't see any obvious damage when I dismounted and examined the fuseholder. I threw it in the garbage and replaced it with another of the same type but, this time, I connected it in the negative rail, where it's safe. The terminal near the mounting collar is now grounded and the terminal at the other end of the fuseholder goes to the negative supply, to prevent a similar insulation breakdown from recurring should the fuse ever blow or be removed with the power switched on.
  Reply With Quote
Old 10th December 2004, 11:17 PM   #52
diyAudio Member
 
cogsncogs's Avatar
 
Join Date: Jul 2003
Location: Wayne, West Virginia
Quote:
originally posted by: ray_moth
I connected it in the negative rail, where it's safe.
Yes, this would be the preferred location in this instance. It's not only the fuse holder, it's also the voltage rating of the fuse itself. The highest rating I've seen IIRC is 250V. If you could find one that's rated at 500V, a pigtail/axial mount type that you solder in place ie like a resistor, you could use it in the HT rail. But I would still prefer to use one in the ground-negative rail closest to the pwr tran CT or the neg terminal of the bridge rectifier...if used.

Wayne
  Reply With Quote
Old 11th December 2004, 12:59 AM   #53
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally posted by Layberinthius



This dust guideline is great advice for people wishing to place vent holes around the Octal or even 9pin vacuum tube sockets, It could build up /just/ inside the vent holes and over the top of the terminals of a socket, hypothetically creating a nice flame through the top.

quite anecdotal -- I would pick up broken TV's in the 1960's and gut them for the power transformers, tuners etc. in ham radio gear -- many a black and white TV could be brought back to life with a good vacuuming. i still have a "Madison Fielding" receiver which was supposedly in bad shape -- it required both vacuum and air -- best damned sounding receiver I have!

with "respect to respect" for HV -- I saw a newsgroup item years ago from one of the scientists at Oak Ridge TN -- seems that he got too close to a Kepco 2kV supply and received a shock which knocked him to the floor. could have been the relative humidity or whatever. forewarned is forearmed.
  Reply With Quote
Old 16th January 2005, 01:17 AM   #54
raypsi is offline raypsi  United States
diyAudio Member
 
Join Date: Jan 2005
Location: middle earth
It always has been and always will be; mils that kills and volts that jolts. It always is milliamps of current that will kill you. And the Voltage will jolt you. But if you get jolted and sustain head trauma when you bang up against the wall. That could kill you too. They taught us always keep one hand in your pocket.(grin) Although I know of a person that used the AC main across his chest to di fib his heart and it saved his life.

I remember once I grabbed a 5,000 VDC focus voltage line by accident and I couldn't let go. It wasn't until my knees gave out and fell to my knees on the floor that I let go. Went right through my shoes, lucky focus voltage doesn't have many mils
__________________
semper fi
  Reply With Quote
Old 19th February 2005, 06:05 PM   #55
jwatts is offline jwatts  United States
diyAudio Member
 
Join Date: Jan 2004
Location: Erwin, Tennessee
Default 5KV

I was in an Atomic and Nuclear physics lab once and the guy I was with politely rested his arm on two binding post on a 5KV power supply. Needles to say he hit the ground but recovered. I have a retired uncle who has been repairing and building tube radios since the days of tube radio and he once told me you can withstand a considerable amount of voltage as long as the voltage doesnít travel a long distance through your body such as from the front of your finger to the back of your finger. The guy in class produced a closed circuit only a few inches through his arm. Iím not saying go and see if you can take a big hit, but if you do accidentally get hit if possible try and route it a short distance.
  Reply With Quote
Old 11th March 2005, 06:24 PM   #56
Gluca is offline Gluca  Italy
diyAudio Member
 
Gluca's Avatar
 
Join Date: Nov 2004
Location: Back to Italy
Just a tip from a newbie.

I do always test my projects with low voltage first whenever applicable: I have a 12V SLA battery and a 230V:12V small toroidal trans for AC testing.

I feel much more confortable this way.

Gianluca
  Reply With Quote
Old 2nd April 2005, 04:22 AM   #57
diyAudio Member
 
Kofi Annan's Avatar
 
Join Date: Jan 2004
Location: US
I'm just your average UN Secretary General trying to learn a hobby. I always check and bleed the PSU caps before working on an amp and I always make sure I'm working with one hand only when testing voltage on a live circuit.

I felt like I was pretty careful overall until tonight.

The PSU on a phono preamplifier I was working on was smoking (shorted the PSU by accident) and I was reaching for the toggle off switch rather than pulling the plug. The B+ wasn't even connected, but when I reached for the off switch, I accidentally touched the live B+ (385VDC) with one hand while bracing against the chassis with another.

I felt the caps drain across my chest.

I'm feeling pretty lucky tonight and I will never forget this. I know that this probably wasn't enough to kill me, but it scared the snot out of me.

Please be careful.

Kofi
  Reply With Quote
Old 2nd April 2005, 05:51 AM   #58
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
[QUOTE I accidentally touched the live B+ (385VDC) with one hand while bracing against the chassis with another.

I felt the caps drain across my chest.[/QUOTE]


Hi there.....you were lucky on that accident...basically recklessness.....however I'm telling you off....you were lucky to get away with the Joules stored in the CV product............When I was in TV servicing in the 1960's....there is a golden motto......Always keep the other hand in the pocket when doing high voltage work. Never complete the body electrical circuit with both hands on metal cased equipment ---> Being zapped is a wicked experierence.......Arrange your work bench in such a way to minimise this sort of thing happening again. In the back of ones mind always beware of the grasp effect .....of not being to release from the source because of musclar contraction.

I have a < dead mans switch> on my bench, a mains rated AC toggle to disable the line supply.....(the red capped mushroom button one sees on so many industrial working equipment).
An AC earth leakage protector (RCB) wouldn't have saved your day on this one....If you work with high stored energy like I do.....and live alone .....the awareness.......is the same.....don't drink and drive electronics.

richj
  Reply With Quote
Old 2nd April 2005, 11:39 AM   #59
diyAudio Member
 
Kofi Annan's Avatar
 
Join Date: Jan 2004
Location: US
Quote:
Hi there.....you were lucky on that accident...basically recklessness
Agreed.

Quote:
Always keep the other hand in the pocket when doing high voltage work
I always have, but I had a moentary lapse of reason. Almost cost me my life insurance policy.

Quote:
Arrange your work bench in such a way to minimise this sort of thing happening again.
Working on that today.

I posted this so that I would get admonished for my poor judgment and so I would have a permanent record of last night. Being in the business of international crisis resolution, I'm a naturally paranoid and careful person. I've alway overdone it on the safety end. But this time I admit that I had been working on this project for a while and I was... tired. Guess I didn't notice it or didn't want to believe it at a minimum.

I'll be stopping for the night much earlier in the future...

Kofi
  Reply With Quote
Old 2nd April 2005, 01:19 PM   #60
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Kofi -- when you retire (or are forced out) you can take a job here in The People's Republic of New Jersey -- there is a scam going on which would need Annan's expertise -- I think it's "oil for mozzarella" or something like that at any rate, we are thinking of settling the Darfur refugees in Newark, Paterson or Camden so your expertise is in much need and I am sure it would be safer than testing power supplies in vivo
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Workbench safety practices? Stormrider Equipment & Tools 3 3rd August 2008 05:08 PM
Safety with high volts: 101 rick57 Tubes / Valves 34 1st April 2005 04:51 PM
Safety Practices, General and Ultra-High Voltage DrDeville Everything Else 49 23rd September 2004 09:31 AM


New To Site? Need Help?

All times are GMT. The time now is 06:41 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2