A RUDE Awakening ! ! !

[The Slab Bacon]

I had a good one happen to me Friday evening, And I thought I woud share it with youse guys. (So you dont have the same misfortune!)

After tying the ribbons on the "whatz fah dinnah" net friday, My 4X1 transmitter had a pretty healthy crapout. It blew the plate supply primary fuse, so I stuck another one in to see what had happened. This time there was arcage, sparkage and smokage!!

I opened the back of the cabinet and shorted the power supply OUTPUT caps and grabbed my meter. Next thing I knew there was a loud CRACK followed by a blue arc and a chunk of skin had been blown off or the first knuckle of my right thumb. Luckily, and by the grace of God I got it all just in one hand. My left hand was in my pocket and I was wearing rubber soled shoes. I JUST GOT NAILED WITH 3600VDC! ! !

After regaining my composure, (and checking my shorts) I found the problem. The 40lb, 1940's vintage Kenyon choke had went open on me. It is one of those grey potted cubes. And I run this thing cap inpoot (C-L-C) to get a little extra voltage.
With the choke now open, the inpoot cap was never bled down and still holding 3600v ! ! ! ! ! When I hit it with my thumb, it let out a crack that sounded like you hit it with a grounding stick. Luckily I got it all just through my hand. If I would have got that through my chest, I know it would have killed me! ! ! ! ! ! So I am just missing a chunk of skin from my right thumb knuckle instead.

So guys, please learn from my stupidity!! Dont be complacent, take a shorting stick and check every HV cap in the rig BEFORE sticking your hand into it!!

FWIW, the choke has been replaced and the rig is back up and running. The shame is that that choke has been in there for 10 years!!

                                                                      The Slab Bacon

[WD8BIL]

WOW! Good lesson at your expense, Frank. Sure am glad it wasn't worse considering what you've been through this year.

I listened for the WFDN every afternoon last week re-couping from wrist surgery. I could hear carriers with the BFO on but there's just no propagation now at 5PM to the west end!

See yawl next season!

Glad you're still with us!!

[W2ZE]

Frank,

So sorry to hear of the misfortune of the 3600v lesson. A jesus stick is installed on all of the big rigs here. Touch all the terminals of every cap in the HV supply, then lay it across the output of the supply. Mnay braodcash tx's not only have them, but have interlocks on the clips that hold them in place. One can be made by simply using heavy guage copper inserted into the end of a large wooden dowel, then copper braid slobbered onto the base of the copper where it meets at the dowel. The other end connected to groundium. Cheap insurance considering the consequences.

Mike

[flintstone mop]

WOW I thought that I was being paranoia by stroking every component in the PS, diodes,caps,choke,secondary of the transfromer, with my Jesus stick.
Frank that must have been an ugly medical event, when those volts pop out of another part of your hand.
That TX has seen some good service.

Fred

[David, K3TUE]

So glad you're alright.

[WB3JOK]

I'm happy you survived!
But keep a close eye on that hand and forearm... high-energy electrical injuries can cause damage not immediately apparent. If it starts to swell, turn cold or discolored, etc. get to an emergency room without delay.

[k4kyv]

Good point regarding the jesus stick. Just letting the bleeders take care of it as you watch the DC plate voltage meter slowly drop to zero doesn't cut it if the choke opens or a connection comes loose, although with a single-section choke input filter that shouldn't be a problem.  I prefer to use about 1K of resistance (WW power resistor) in the stick as a preliminary bleed-off before dead shorting the cap.  If it does happen to be fully charged, the surge from a dead short can destroy the capacitor by opening it internally.  It could even be a safety issue in case a blob of  molten metal hits you in the eye.  But just using the resistor alone poses a risk in case the resistor opens up, so best to use resistor first, then dead short just to  be 100% sure.

My lucky-to-be-alive moment occurred about 2 AM in 1960, the night after the presidential election, while everybody else in the house was asleep. I had stayed up late listening to the election returns on the radio and decided to work on the transmitter. I got 1000 volts from hand to hand from microphone to ground and couldn't let go. The makeshift mod transformer I was using shorted from primary to  secondary and I hadn't grounded the modulator.  I got zapped holding the mic in one hand and touching something in the transmitter with the other. Luckily I backed away with enough force to pull the mic cord right out of the connector.  Otherwise someone would have found me hanging on the thing the next day.

Glad you are still with us, Frank. Or should I say glad we are both still amongst the living?

[W3GMS]

Frank,
Glad you survived the mishap OM.  A good leason from the open choke failure mode.  I know a lot of us just short the HV output to ground when we are working on the gear, but you bring up a great point about the filter choke failure.  The HV meter on the output of the supply would make things look "safe" but that is not the case.  I do as Mike mentioned with the shorting stick.  I have been hit with HV to many time in my younger days and learned my leason big time.  No room for error around HV. 

Don,
Make sure those WW resistors in series with the shorting stick don't open up.   I understand the purpose but I would be inclinded to measure the resistance of that assembly every time I used that stick! 

Regards,
Joe, W3GMS   

[KE6DF]

Probably would be a good idea to put a bleeder on the input capacitor in a CLC filter. A high value like 1M would bleed it down even if the choke opens -- and at the same time not waste too much power.

Working with high voltage and hand gun target shooting are two hobbies that have one thing in common. You can't afford even one serious mistake.

[K1JJ]

Probably would be a good idea to put a bleeder on the input capacitor in a CLC filter.

That sure got my attention Slab!  

Glad you're OK.  The wound was probably cauterized with no blood expelled at all, right?  I had it happen to me in 1972 and it didn't bleed, but the ripped open flesh got infected over and over for about a month. I should have had stitches.

Yes, in addition to the Jesus stick, it's a good idea to put extra mini bleeders across ALL HV caps. I did it in Fabio - even the Heising cap has a mini-bleeder. For 3600V, you would need at least  ten 1/2 watt 100K's in series to handle the voltage to prevent arc over.  Maybe mounting them on a small perf board would work.

Keep an eye out for infections, OM.

T

[Opcom]

I'm glad you wre not hurt worse! A picture would drive the lesson home better for those who are new and might not believe how serious this is, but only if you are comforable with it. The open choke is one of the things warned about in the old books, but it is so rare. I hadn't thought of it in forever.

[KE6DF]

. For 3600V, you would need at least  ten 1/2 watt 100K's in series to handle the voltage to prevent arc over.  Maybe mounting them on a small perf board would work.

And there are resistors like this available also:

http://cgi.ebay.com/High-Voltage-Power-Resistor-1M-1-12W-40KV-Electrohm-/170496829233?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item27b2672731

[K1JJ]

And there are resistors like this available also:

http://cgi.ebay.com/High-Voltage-Power-Resistor-1M-1-12W-40KV-Electrohm-/170496829233?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item27b2672731

Yep, those look perfect for the job.

T

[w4bfs]

being vertical beats being hortizontal

[Todd, KA1KAQ]

Those nets will lull you into a sense of complacency. Beware! 

You got off easy, Frank. Considering all you've been through in the last year or so, you'd make a cat with 9 lives nervous. Glad you are okay and here to relay the event and its causes.

Mike, thanks for the reminder of the Jesus stick. Meant to build one of those a while back and never did. An excellent project for these 95 degree days.

[W3GMS]

Bleeders are good, but never rely on them to be working.  In a large series string all it takes is one resistor to fail and you have a false sense of safety.  Those wirewound ones with the slider taps are the worse.  They tend to open up right where the slider is.  I use to use the slider as a tap for a scaled voltmeter, but never again after almost being killed when I was 14 with that scheme.

Really the only way to be sure you have everthing at zero potential is to take the stick and make sure all is discharged. 

Regards,
Joe, W3GMS

[W9GT]

Hey Frank,  Sorry to hear of your shocking experience!  Anyway, glad to hear you are OK.  A friend of mine had a very similar experience with an old 4-1000 amplifier.  He went to the hospital ER for treatment and ended up with a secondary staff infection which darn near cost him his hand....I guess sometimes they (hospitals)  do more harm than good.  He recovered OK, but it was a lousy experience.  Take care and watch out for infections, as mentioned by others.

73,  Jack, W9GT

[K5UJ]

One of the first things I did as part of my amp project was make a chicken stick with a metal hook and pvc pipe and copper braid.  I put a big 13 ohm wire wound resistor I had on hand in series near the hook.  Frank sure glad you are okay.  that would have puckered me right up and made me think about QRP (for a few minutes). 

Rob

[The Slab Bacon]

Yea, there is a large degree of butt pucker factor with that power supply. When the line voltage is good (cooler days) it is not unusual to see the no-load voltage get up to 3750v or higher. (with 200w of bleeder load in place) and then settle down to around 3400 under full load. So I am naturally a bit apprehensive when going in the back of the cabinet.

that thing ran like a swiss watch for around 8 years, then it has been one power supply problem after another. But I'd have never thunk that choke would open up. It has been the rock of Gibraltar for all of these years. An insulation breakdown failure would have been easier to take, but not a dead fail open. Itz just one of those things that just doesnt happen. (except to me) also keep in mind that the plate transformer is out of a BC-1 Gates, so current availability is just not an issue.
Now the choke is a 10 Hy @4kv @1A CCAS out of RCA BTA-1S.

FAIL NOW- - - -SUCKER! ! ! !  

I prolly should run it choke inpoot, but that inpoot cap is good for at least another 400VDC to the plate of the 4X1 under load. That aint hay! And besides I grid block the final and have a step-start when I flip the HV switch.

Rob: LIFE IS JUST TOO SHORT FOR QRP! ! ! ! Once you've had big power you can never go back to being a piss-weaker! I'm just too ornery!

                                                                 The Slab Bacon

[WBear2GCR]

I wouldn't rely upon that resistor to stay together after a single use... I put one together with a higher ohmage myself...
but I am wary. Thought about putting a neon bulb + dropping resistor across it too...

                   _-_-bear

[The Slab Bacon]

In the midst of the last old-buzzard post I forgot one thing.

The main reason for starting this thread was to help prevent someone else from falling prey to my misfortune!

GUYS, STAY SAFE AND DONT BECOME COMPLACENT

[Ed/KB1HYS]

Glad your OK man.  That must have HURT! 

[W3RSW]

Boy Frank, your sure have had a string of interesting life experiences.
Glad your FB OM.

I wonder: if you'd commonly shorted only the output caps all this time, maybe the excessive current from the input caps during several Jesus stick discharges is what weakened the choke in the first place... 

[KE6DF]

Also, if the choke suddenly opened, you would lose power to the transmitter, but I don't see why that would blow a fuse.

Or why you would have smoke and arcs when you replaced the fuse and powered it back up.

Makes me think something else is wrong.

Perhaps the choke shorted to ground and that caused it to burn out and open.

Or perhaps there was a short or arc over somewhere on the xmtr side of the choke and caused the fuse to blow and perhaps blew the choke also.

I'd look at things over a bit more to see if there were signs of a problem somewhere else before the same thing happens again.

[W1RKW]

Frank,
I can relate to that 100%.   Back when I was developing GORT and his plate supply I did the same exact thing.  I was troubleshooting a problem and managed to get the back of my hand which was up against the chassis and my thumb on a 'hot' capacitor, just brushed it.  Best I can figure was about 2.3kV.  There was no bleed down so the caps were hot as can be.  Blew a hole in the end of my thumb.  A flame shot out of it. Think of a pickle across an AC line. My thumb glowed for a split second.  If it wasn't for the back of my hand touching the chassis I wouldn't be posting this.

Man, did it hurt. Funny thing is,  I"ve been shocked on lower voltages and have felt my heart jump a few revs. In this case it purred right along but my hand and arm hurt like hell. I remember my arm going back behind my head.  I developed an infection in the thumb.  Had to have it cleaned out.  So watch it.