The AM Forum

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

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!!

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

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

:o
So glad you're alright.

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.

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?

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   

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.

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

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.

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

being vertical beats being hortizontal

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.

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

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

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

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! ! ! ! ;D  ;D

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

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

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

Glad your OK man.  That must have HURT! 

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... 

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.

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.

I wonder if that choke is what was eating your plate iron. I remember going through intermittent HV crapouts on one of my KWS1's before I finally found out that the choke was leaking and arcing to ground (a common problem on them) I figured it out before I lost the plate iron. I have a spare Stick out of one of my bcast xmitter salvage episodes--Shall I Stick it in the Mail? I think it is a Continental.
Skip

You mean the 13 ohm w.w. in my chicken stick or something else?  not sure which R you talking about.  I guess I used the low value because the service line in-rush resistors are around 10 ohms but of course the line v. is very low compared to what's on a charged filter cap.  I guess it should be somewhere around 500, 1000,  2000 ohms.  For my p.s. 2K would discharge about 2A. I will root around and find another resistor amongst my hamfest goodies.

Sorry to hear about that Frank. I too have been hit. As mike said, a Jesus stick is the way to go. The wire on the stick should be insulated. The end that connects to the chassis should be bolted on. No crimp connections on the lug that connects it unless it's soldered!!

All I can say is WOW !!!!! Sure glad it didn't go through something major - not a good time for a funeral.

Thank God it happened the way it did.

Even though there's only 130VDC in the class E rigs, I'm careful has heck.  I too have had one of your experiences, Frank, and it changed me forever.

Glad to hear your FB OM.Now you know why I was sceeered to neutralize the 6146's on my 530 !

Thanks for sharing Frank.  Your comments may well save a life.  I know I will be more careful now!

Holy Hornswaggles Frank! Good thing you weren't wearing Brent's crotchless chaps...

WOW!! Thank God your ok Frank :P

Brent

What are the specs and size of the choke Frank?

Most here are only 500mA but maybe there is one around @ some of my friends.. But I guess that size rig uses a >1A choke. There is a nice 3.5A 3H 7500V choke at the Black Hole, probably from the 5KW RCA rig.

What does it even cost to buy a new 1A choke any more now? Maybe it is time to think about the 30-60 year old chokes many of us treasure and use. They are getting older, corrosion my be taking its toll, etc. Not to discard them, but to figure out some way to safety the choke if it opens. What fails overvoltage shorted? 100V disc capacitors were mentioned in an old radio book for use on 1200V circuits. Silicon rectifiers?  Also, how to have a telltale the choke has opened? A telltale for the cap being charged might be a string of 1m resistors and a neon lamp.

Maybee its time to rebuild some of the older iron.....  dubya zee ?

klc

I never got tied in to that much voltage/current. I did get hit rather hard with 850 volts or so when I had my old HT32B Halliscratchers rig. One hand was holding open the flip up lid and the other hand reached down to pull off a plate connector. That one had to go right across the ticker. Good thing I was young at the time.

Glad your still here.

Actually, "bleeder" resistor is a misnomer.  Its purpose is to maintain a minimum  load on the power supply to avoid excessive voltage surge under light or no load.  It should not be counted on to bleed the filter caps when the supply is turned off and that was never intended to be its primary purpose.

Thanks for the refresher course Frank. Glad you're okay.

As far as the 'mini bleeder' Tom JJ suggests it might be a good idea to avoid carbon film and metal film resistors. I've seen a number of unexplained failures (open) when these resistors are used in high voltage applications - even when used within their ratings. Perhaps the problem stems from unexpected surges. Whatever the reason, I haven't noticed this with carbon comps. 

Thank God your OK man. It could have been a lot worse. Years ago, a close friend of mine got bit hard from one of these TMC 750's (3000V no load) from his hand to his knee as he knelt down to adjust the modder idle current. He got lucky because he wasnt 'grabbing' anything, and just fell away from the transmitter. He was totally paralyzed from the neck down for about 10 minutes. He tells me this story every once and a while probably with the purpose of keeping me scared. I check everything now EACH AND EVERY TIME i stick my hands on a HV suckply. There was a story floating around years ago about an old timer that got zinged from a Valiant he was working on. As it goes, his wife called him upstairs for dinner some time after that, and while eating, he fell off the chair dead.

Staying scared of what you can't see hiding in these supplies will keep you alive.

thanks, Guys!! I still think the saving grace of it all is that I got ALL of it just through my right hand only. Dont get me wrong, it hurt like hell, but I didnt get any of it through my body. This time I didnt feel any heart palpitations or anything like that. It did scare the livin szht out of me when I saw that arc go to my thumb and heard the loud crack. after cleaning out my shorts and regaining my composure
(about 10 minutes) I had the meter probes back in my hands and continued on troubleshooting. (By the previous symptoms, I thought I fried out the plate choke) Who'd of ever thunk the filter choke failed open? ?

But like Patrick said, it might just be time to thoroughly examine some of this aincient Iron that we are using and covet so dearly. I have never had a choke fail open before. I have seen plenty of them with insulation failures short to ground, but never totally open. I think mine just opened up from the current load of the 4X1 plate. (about 1/2A @ carrier) It was a 1/2A choke that was easily 60+ years old, potted or not. Being potted, I always felt that it was much less suceptable to moisture damage from age and time. Not to mention that that I HI-POT tested it to 3500VAC about 10 months ago (while changing out the plate iron) with absolutely no sign of any leakage. (I usually test anything HV with a HI-POT tester before installing it)

Like I said before, I posted my misfortune as a reminder so others would be wary and not repeat my misfortune. Like I have said many times to many people: "High voltage has absolutely no respect for you, so you have got to respect it! ! ! ! ! ! "
Or like my parents used to say just before they were goin to wail the tar out of me:
"When you dont listen, you gotta feel!"

After crunching a few numbas, I think something around 5 meg for each cap safety bleeder resistor is in order for each oil cap. I allready have 2 50K 225W large dogbones in series for the main bleeders.




NOW, THATS QUITE A MESSAGE! ! ! ! ! !  :o  ;D

As far as the wound goes, I will keep a close eye on it as I am a bit succeptable to infections due to the fact that I am diabetic and have liver disease as well. But.............I'm a tough old bird, and it will take a lot more than this to get me down.

                                                             The Slab Bacon

Brent,
        It blew right after I signed with you, friday evening. After you tied the ribbons on it, I gave the PTT a quick click, click and it went bang and blew the primary fuse!



Hmmmmmmmm...................I wonder if he has crotchless panties to match?  :o  ;D

Some questions are best left un-axed!!!

Woof, a thorough reminder  :o

I work with hot line V. too often and pay with a chomp once in a while. I still work with one hand ( when I can ) but I'm thinking it's a bad habit now that I'm probing around HV again. I'll heed the Slab Bacon warning.

My only real hit was from a rcvr. B+ > chassis in my damp basment bedroom as a kid.
I was contorted and trying to lift every thing onto a new shelf and I couldn't get out from under the mess of leads as it zzipped me. I was 11 or 12 and didn't know from grounds on a cheap, bare boned, tube, SW chassis.   

If my parents knew the hazardous situations I put my self in as a kid they would have chained me up.
                                   Glad your all right OM.

Didn't the chief engineer of WKBW get killed back in either the '60s or '70s - and then there was old Ralph W2WME who got it while working on a linear, I beleve.  So glad Frank wasn't another statistic.

Wow!  Thank God you're OK Frank.   I don't wanna hafta travel back to the states for a funeral!

Steve....
I sure remember Ralph.  We were all surprised when he got hit and did not survive.  I think he was working on an SB-220 linear amp at the time. 

I am not sure about WKBW chief engineer. 

Working with HV is a lot like tower climbing.  If you take short cuts it will get you.  That true of a lot of things.  Look at boating and aircraft accidents.   We tend to get very comfortable with things we work around. 

My Dad into his 80's would put the extension latter up and re-shingle the roof.  Then one day he took a shortcut and fell while doing something much easier.  He crushed all the vertebras in his back.  Struggled with the pain for several years and then gave up.  He was dead a month later.

Regards,
Joe, W3GMS   

wow.. Glad your ok! 

C

Yo Frank,

Good thing you're OK,  sure would hate for you to never hear my imaginary 813 ;D  Having said that,  at the rate I'm building the 813,  you'll be with us for a long time.  I have also noted that you have had some other health issues over these past months.  I wish you well on all.

A HV choke opening up like that is not too common.  It probably shorted to ground internally.  The short fused open the winding, most likely near the terminals.  One reason I don't like potted chokes or xfmrs.  They develop carbon shorts through the potting tar, usually near the terminals.

You being zapped by the input cap is a very good reason to not use cap input filters.  The choke opening up left the input cap fully charged with no bleeder current.  You can always have separate bleeder resistors across each cap.

Don't short circuit yourself,  I'll talk to you on 75M.

Fred,  KA2DZT

Fred,
       I would not have used cap inpoot if I didnt need it to get the voltage I wanted to keep the 4-1000 happy. Sometimes you just gotta do what you gotta do. I like to have as much "fire in the wire" as I can.

I could not be happy making others have to listen to my piss-weak 51watt signal.
Remember the first rule of the piss-weaker: "the weaker they are, the longer they talk"

BANG! ! !  LOOKIE HERE, SQUASHED JUST LIKE A BUG  ;D  ;D  ;D


Hi, Fred  ;D  ;D

(I probably wont live long enough to ever hear the "imaginary 813 rig")

Nah, we just need you back here to have some more big signals on the WFD net ;D

glad your ok !!!! We don't need our bacon extra crispy!!!!

Wayne
KB3RRX

Although this isn't the best insurance to guarantee a PS is discharged but putting some sort of indicator on the outpoot is helpful.  The 813 rig here has an HV meter tied right at the HV cap so I can at least use it as reminder to wack it with a discharge tool.  I didn't have that when I got wacked way back when.

And Frank, as I stated before, watch for infection.  When tissue is damaged deep within you're open for infection. Make sure you watch it.  It caught up with me and I had to have my thumb opened up.

Bob,
       I guess I just got lucky. The hole is has closed up nicely, and all the signs of imflamation are gone. It is just a hard crusted, caloused scab with no signs of redness anymore. I guess it just cauterized itself when it happened. It is actually healing rather quickly, considering that I am a diabetic. Many thanks for the concern.

Hi Frank,
Still watch it though. The wound has the potential to turn on you.   I thought I was healing nicely too but weeks after the thumb started throbbing and then the wound started what looked like a small blister but deep blister with discoloration, painful too.  I lost part of my thumb nail for a short period due to them cutting it open. But other than a small scar where they went into the side the thumb all looks normal now.  I guess it all depends on how the current flowed through the tissue.  Hopefully the current flow was at the surface and affected the surface tissue rather than deep down. 

In reading up on what happens with electric shock, the shock results in nectrotic (dead) tissue.

The dead tissue is not necessarily at the surface, but can be deep inside.

So, the external wound can appear to heal, but several days later, the dead tissue starts to rot and causes a deep seated infection.

In extreme cases, people have survived a major electric shock, and then died days later from necrosis of internal organs and tissue.

Bob,
        Looking at it today all seems very well. (2 weeks after the fact) It is healed nicely with no discoloration. Just a small scab and a hard calous. So I guess the burn damage was mostly on the surface. As a matter of fact the calous was so hard that I took some sandpaper and sanded it down the other day. There is no discoloration and it even now perfectly matches the rest of the thumb in color.  I think it just blew the bark off of the surface. I dont usually infect easily.

Many thanks for everyone's concearn, but I think this drama is over. All is well that ends well. I just wanted to possibly save someone else from my misfortune. Thanks to all! !

                                                                              Frank