Electrocuted by Can Capacitor

[GussyLoveridge]

Folks -

I'm about 10-12 years into working on tube amps and today I got my first good shock. Surprisingly, my hands were not in the amp, nor was I using any tools. My hand brushed up against the outside of two or maybe three of the can style filter caps and I got a pretty good wallop.

I don't really understand what happened. The amp was plugged into my dim-bulb which was plugged into my variac.

Speculate?

Thanks,

Gus

 

[emrr]

Series can for higher voltage rating, so you touched 50% value of total potential? Usually that’s an insulated case.

If someone has the bright idea to disconnect ground on a can cap for mechanical reasons when recapping, then wiring positive of new cap to positive of old, with the new cap grounded, the old can cap case will now be floating at full voltage, and will at least tickle if not bite.

 

[Tubetec]

I managed to get a jolt across my chest yesterday handling a pcb with a high voltage cap on it , the board flew across the room ,but I was fine . Ive got a few shocks from live 240volt mains over the years ,it will leave your nerves jangling for an hour or two , of course if you become the short with one hand touching live and the other neutral your in much more serious trouble .

 

[CJ]

I get a jolt about once a week.
Free electo-shock treatment me thinks.
DC will push you away but AC will make your muscles contract like those shock boxes in Tijuana. You get your drinking buddies to form a series circuit and the first guy to let go buys the next round. But since quarts of Carts Blanca were 75 cents back then, it was no big deal. You could feel your hair rise up and your eyeballs ready to pop.

Now if you are working on a 200 KV power line in the rain and wind then you got something to worry about.

I don't consider it a good jolt unless I smell burning skin.

 

[Tubetec]

I once made direct contact between live and neutral across the tip of my finger , the good thing was it automatically cauterised the tiny puncture marks caused by the spark .

 

[JohnRoberts]

Lawnmower spark plug magnetos could make memorable shocks. On the old mowers that was how we shut down the running mower with a metal shorting contact. If not careful you could slip and touch the wire with your hand.

JR

 

[musika]

Get a nice cigar and a shock for a few pesos... turnout up to ten (or eleven).

Shock Vendors

 

[JerryPbury]

Lawnmower spark plug magnetos could make memorable shocks. On the old mowers that was how we shut down the running mower with a metal shorting contact. If not careful you could slip and touch the wire with your hand.

JR

Been there, done that on mini bikes in the early sixties. When I was about 10 I caught 100,000 volts off of a black & white TV tube. Felt like my hand had been hit with a giant wooden mallet! 120 AC occasionally tickles me several times a year, more now that I’m older…….

 

[Westrek]

I've been shocked numerous times. I guess my heart's pretty good! My cat was on my bench one day sniffing around and happened to put his nose on the screw of a big can cap. He jumped about a foot in the air and made a quick exit!

 

[Tubetec]

One of my dogs recently chewed on some out door electrical cable , the job wasnt done right in the first place as armoured cable should have been used as well as the cable burried in the proper spec pipe , Luckily I spotted the damage and was able to remediate the damage with extra insulation and self amalgamating rubber tape on the outside . Doggy was fine but she could have very easily been killed , she wouldnt have stood a much of a chance with paws directly on the wet ground .

And yeah ,before some wise ass, know it all, sparky the fucking clown tries to have a go at me for having a sub standard installation , it wasnt mine ,it was at a friends house . Im not in the mood to be triffled with TVM

 

[Ivan K.]

If you really want to know...measure between chassis ground & the Cap cases.

My intro to electronics at age 10 was plugging in a 10kV oil furnace ignition transformer and having a lead land on my leg (I was in shorts), and contracting my leg muscles to propel me all the way across the room and hit my head against a wall and seeing stars for a minute or two.

Not content with one lesson, I hooked 1 lead to a long wire antenna and the other to ground and wiped out radio & TV reception for several blocks-upsetting the neighbors. I was envisioning them coming for me with pitchforks and torches-not the kind with batteries so I quit.

 

[Brian Roth]

Not content with one lesson, I hooked 1 lead to a long wire antenna and the other to ground and wiped out radio & TV reception for several blocks-upsetting the neighbors. I was envisioning them coming for me with pitchforks and torches-not the kind with batteries so I quit.

Sounds familiar! I was maybe 10 YO and tried something similar with a model-T spark coil unit I bought via mail order from JC Whitney. I may still have that device in my stash of "useless parts".

Bri

 

[Tubetec]

Was a tough day for several reasons , shit happens ,
Im not beyond a joke or a laugh at my expense , if fact I often disarm detractors by sending myself down in flames better than they can , then when I have them off kilter I come in with a killer blow ,metaphorically speaking , really throws um ,

I got a Led panel security light today from Lidl , it has a seperate solar panel with a 5m cable ,
I was able to place the light in the attic so the sensor automatically switches it on when needed , that keeps two hands free for stability on the way up the ladder ,instead of needing a torch in one , the solar panel mounted up on the south facing facia boards , the whole system is IP65 sealed so should last for years .
The other thing I did was attach the light to a wooden beam with a clip , so once your up there you can unplug the light from the panel ,unclip it and use it as a lantern . The sensor has the usual adjustable on time, sensitivity and threshold controls and 50 x 0.2W leds , lasts around an hour on a full charge . Im not 100% sure how it will handle our usual grey Irish winter with very little direct sunlight , I'll probably charge the lipo cells fully via my RC hobby charger ,so the panel should have no bother keeping the cells topped up over winter .

 

[jfkelliher]

I was taught that failure to discharge caps on tube amps prior to monkeying around inside can get you electrocuted, as in dead. Everyone's tolerance to electro shock "therapy" is different. Please find a good how-to video on you-tube and take heed. Oh wait. You've been monkeying around inside of tube amps 10+ years and had it powered on and hands weren't inside...oops, Nevermind.

 

[Tubetec]

10 years , more like 30 years + I've been messing with high voltage ,
probing high voltage nodes with one hand behind your back is good practise , that means the current doesnt cross your chest and stop your heart in the event of misshap . Tesla demonstrated conducting tens of thousands volts through his body close on 150 years ago , the only injury he suffered was the tiny pin prick where the spark hit .
Raw mains power is many orders of magnitude more dangerous .
By the way JFK how can you fix your tube amp and make sure its working properly or not if you havent the balls to check voltages with the thing energised ?
now, stop talking through your hat , you wouldnt like me when Im angry

 

[Mworthin]

Getting back to the OP…He brushed the outside of the metal can, which should be grounded, and got shocked. If that is the case, it sounds like there is a short there that should be fixed.

 

[ccaudle]

My hand brushed up against the outside of two or maybe three of the can style filter caps

Without any information on the model of amp or a schematic to check, my first fear would be an old style "hot chassis" amp which does not have a fully insulated line input. Or if the line input is intended to be isolated, possibly a shorted high frequency filter cap. "Line input" in this context meaning power line of course, not line level audio.

 

[Valveamp 101]

I would definitely do some voltage testing (maybe start with unpowered ohm readings) from can case to chassis, etc. That sucks.

When I was doing industrial electronics I got hit with 480 and 240 3 phase VAC each once....both times I was under the weather and should not have gone to work. I don't make that mistake anymore.

 

[GussyLoveridge]

Amp is a Garnet Session Man - there are 5 x 4 section 20/20/20/20 uF @ 450 VDC can caps for the main filters. The power cable is a properly grounded 3 prong and the so called "death cap" has been removed from the circuit.

Thanks for the advice. I will check for potential between the cases and the chassis.

 

[GussyLoveridge]

The first four section caps are run together and then in series with the next. There is some 550 VDC on the first can - the second can is grounded. Half of the voltage on the first cap is showing up between the case and ground. Same with the next pair.