Man survives 2000 volt jolt.

[wa2zdy]

.

And finally...I commute on the New Haven line of Metro-North, and their catenary supports say "Danger - 11,000 volts".  Does anyone know if that's what's on the catenary itself, or is that referring to the other feeder wires up higher?  The insulators on the catenary sure look like they're good for 11kv.  I guess there's lots of stuff in the cars to protect the riders from that.  The other branches of Metro-North are either 700 or 600 volts.  The third rail is marked 700 volts, but the cars say 600 volts.  Maybe a 100v drop between the third rail and the car?   

Yes, the trains on MetroNorth and the rest of the old Penn Central system run in 11kv 25Hz AC.

[K1JJ]

Good  summary, Dave! 

You mentioned the secondary fuse.  ie, a fuse that goes in the ~5kv DC line before the amplifier.

What I did here is install a pair of 2" stand off insulators spaced about 2" apart. The HV plus lead goes in series here and the insulators are bridged with TWO fine strands from an RG-213 coax shield.  When the HV supply gets shorted, it opens up with a flash and the tiny wires evaporate. It's imporatnt to keep the insulators apart by two inches min cuz of the sustained arc that can occur.

It has saved my solid state diode bridge rectifier stack many times. In the past I've wiped out bridges, but not one has fried since installing this HV fuse.   

Ther most common short circuit reason?  I hate to admit it, but it's cuz  sometimes when finsihed working on the amp, I forget to take the handcuffs or Jesus stick off before firing it up ...  BANG!! 

T

[Glenn NY4NC]

Yes, thanks for the explain Dave... Yea Tom, I've come across that same thin wire HV fuse method during my recent amp info searching online.

I Guess "Handcuffs" could be made with some sort of metal bar on a hinge that shorts the filter cap bank.

....have you seen this homebrew YC-156 big mawl linear amp??

http://www.wv7u.com/yc156amp/yc156amp.html

Good  summary, Dave! 

You mentioned the secondary fuse.  ie, a fuse that goes in the ~5kv DC line before the amplifier.

What I did here is install a pair of 2" stand off insulators spaced about 2" apart. The HV plus lead goes in series here and the insulators are bridged with TWO fine strands from an RG-213 coax shield.  When the HV supply gets shorted, it opens up with a flash and the tiny wires evaporate. It's imporatnt to keep the insulators apart by two inches min cuz of the sustained arc that can occur.

It has saved my solid state diode bridge rectifier stack many times. In the past I've wiped out bridges, but not one has fried since installing this HV fuse.   

Ther most common short circuit reason?  I hate to admit it, but it's cuz  sometimes when finsihed working on the amp, I forget to take the handcuffs or Jesus stick off before firing it up ...  BANG!! 

T

[YAY-LOW]

The worst jolt I ever got was in November, 1960.  It was election night, and I had stayed up late listening to the Kennedy vs. Nixon election returns on the  radio, and decided to work on my transmitter.  It was about 2 AM, and everyone else in the house was alseep. Lacking a solid ground connection, when the modulation transformer windings shorted between primary and secondary, it put the whole modulator unit at full +1000 plate volts above ground.  I was holding the mic in one hand and went to adjust the transmitter with the other.  As soon as I touched the transmitter, I got the full plate voltage from one arm to the other.  My hands were frozen to the mic and to the transmitter and I could not let go.  I managed to jerk away, and pull the mic cord right out of the connector.  That's most likely the only thing that saved me.  I fell over backwards and broke a glass 6L6 that was lying on the floor, with my head.  I had some significant burns on my hands, and arm and chest muscles were sore the next day, but that was all the damage.  One thing that was probably the most frightening was that when I did get loose, my paralysed arms went completely spastic for a couple of seconds.  If that mic cord had not pulled loose from the connector, someone would have most likely found me hanging on the thing next morning.

Before that incident, I seemed to routinely get zapped with HV whenever I worked on the trasnsmitter.  Since then I have never been seriously shocked, and I often work around voltages as high as +3500 or more.  I suppose experience makes one a believer.

Dayum.  This post oughta be put on the home page of this site!!!

[W2VW]

   

Ther most common short circuit reason?  I hate to admit it, but it's cuz  sometimes when finsihed working on the amp, I forget to take the handcuffs or Jesus stick off before firing it up ...  BANG!! 

T

Done this myself more than once. It shows how easy it is to forget and that all safety systems should be redundant.

[W2VW]

....have you seen this homebrew YC-156 big mawl linear amp??

http://www.wv7u.com/yc156amp/yc156amp.html

Yup. MRI machine meets H.F. amp. Nice stuff.

[W3LSN]

I guess my point is that these protection circuits create a false sense of security for newbies just getting into the hobby...  just wanted to make that point for the archives.

And it's a point well taken, not only for those in our hobby, but for anyone working around high voltage. Coupled with that are dangers associated with bypassing protection circuits or a failure to design them into equipment in the first place.

I worked at one TV station that experienced an engineering fatality due to several of the reasons mentioned in this thread. Luckily the accident happened before my employment there, but I observed that it cast a long shadow over the company and everyone connected to it for many years afterward. Human nature being what it is, these types of accidents unfortunately seem to reoccur every years. I always cautioned any new technicians not to think about themselves, but to think about those they would be leaving behind if they ever considered taking a shortcut on safety procedures. I told them to think about their fellow workers who would have to pull the big switch or the empty eyes of the grieving widow and the fatherless kids. In the case of my station, the employee had bypassed safety interlocks and was working on energized equipment alone without another man providing a safety backup. There was actually a second worker in the building at the time, but he was in another room.  I'l spare the unpleasant details except to say that the second worker never heard the accident when it happened. He was alerted when the smoke detector went off.  The neighbors to the site were alerted when they heard the second man screaming. The nearest neighbors were 1/4 mile away.

We all know that there is no shortage of hubris among some hams. It's easy to become complacent and dismiss basic safety measures whether it be in the interest of time or because we think that somehow we are immune to danger. Somehow we never expect that the ultimate crapout will happen to us when we tempt fate and cease giving high voltage the respect it deserves. I'm not trying to dispense a bromide here, but hopefully to make someone think twice before he does something stupid. Life is far too short as it is.

73, Jim
WA2AJM/3

[Glenn NY4NC]

That's a scratch built amp. Pretty amazing. The only thing from an MRI machine is the surplus tube 
Wish I had that much "scrap" aluminum to play with!

....have you seen this homebrew YC-156 big mawl linear amp??

http://www.wv7u.com/yc156amp/yc156amp.html

Yup. MRI machine meets H.F. amp. Nice stuff.

[W2VW]

More electrocution banter. Good reading.

http://musicradio.computer.net/wwwboard//messages/270193.html