Breadboarding HV Supplies

[N1ESE]

A "breadboarding HV supplies" thread can definitely stand on its own with probably very useful information especially on safety and design.

As a newbie to tube equipment building my first HV system, I agree so I started the said thread here. 

[Pete, WA2CWA]

From W9ZSL:

Well, while breadboarding my HV supplies, I wanted to move my meter which is one of those big 3 KV Simpson model 29's from the BC-1T.  There is a major 3 Meg dropping resistor that goes with it.  This is my "bench mark" calibrated meter.  So I set it up with my 2KV plate supply and decided to move it using the resistor as a handle.  Bad move!  My hand acted as a parallel resistor.  No damage, but it's a damn good thing I wasn't grounded.  Picked it up with my left hand.  If I'm having a heart attack, that sort of stupidity might save my life.  Otherwise, it sure is a wake-up call!  Good thing the body resistance is in the meg ohms.  Gives you a new respect for HV for sure!

[Pete, WA2CWA]

From K1JJ:

Well, while breadboarding my HV supplies, I wanted to move my meter which is one of those big 3 KV Simpson model 29's from the BC-1T.  There is a major 3 Meg dropping resistor that goes with it.  This is my "bench mark" calibrated meter.  So I set it up with my 2KV plate supply and decided to move it using the resistor as a handle.  Bad move!  My hand acted as a parallel resistor.  No damage, but it's a damn good thing I wasn't grounded.  Picked it up with my left hand.  If I'm having a heart attack, that sort of stupidity might save my life.  Otherwise, it sure is a wake-up call!  Good thing the body resistance is in the meg ohms.  Gives you a new respect for HV for sure!

Hi Gary,

Glad you're making progress.


I am a little concerned:

Looking at the picture of your 3KV meter and the 3 meg dropping resistor, it looks like you are using  ~ 600 V insulated wire on both ends and also some enamel covered wire, no?   There is lethal 2KV on one side of that resistor.  I would replace both sides with 10KV+ rated  HV insulated wire.  That is an accident waiting to happen.

You also mentioned holding that 3 meg power resistor, thinking it should be OK to use as a handle.

That was a shocking heads-up experience.  Please carefully review your high voltage safety procedures before working on the rest of that power supply and amplifier.

T

[KA2DZT]

Pete, good post, makes you wonder if some folks should be doing any of this building.  I read it last night but didn't want to say anything.

[W2VW]

There's no reason to poke an energized high voltage supply for measurements, not ever!

Breadboarding imO is a bad idea here too.

It's been about 25 years since the AM commun-i-tay lost a member to electrocution.

Let's keep it going.

There are plenty of people here who will share experience on what to expect from different sets of power supply parts.

One guy named Fred has 32 tons of transformers.

[w1vtp]

These are all good admonitions!!  I offer this article of the renown experimenter Ross A Hull.  The topic of safety while working around high voltage is brought home in the last paragraphs under "Untimely End."  Mr. Hull's accomplishments were great and he was well known as an experimenter extraordinairer.

This is all fun but we need to respect HV.  One rule I ALWAYS use is to never "poke" at HV: with the circuit proved to be "dead," make your connection and then turn on the power supple.  After the measurement is taken, turn off the PS, apply the grounding "jesus stick" to known HV spots and then, using insulation remove the connection.  Some may disagree with this rule but it's one that has served me well over the decades.

The rule that Ross Hull broke was reaching into a circuit without looking - keep yer hands away from HV

GL es keep on learning, Al

[W9ZSL]

Actually, this meter and resistor are from a BC-1T for testing only and isn't being used in projects.  As for my earlier statement, it was less than 450 volts that I was bringing up to 750 with a variac.  I was thinking about it last night when I remembered.  I moved the meter for a better view accidentally bridging the dropping resistor.  No burns, but got a great wake-up call. Good thing it wasn't 2 KV.  Lesson learned: don't touch a thing with the power on.

As far as bread boarding the various power supplies, I've tried many combinations of bleeders and caps for the 813 / 811A amp with no problems because mains power was applied just long enough to get a voltage reading with no load but the bleeder.

[K1JJ]

I've told this story before, but since we're on the HV safety subject.....

I was 20 years old back in August, 1972. I was on a home-brewing roll trying to build a JJ "S-line" of rigs for a complete homebrew station. It was a hot, humid day. My hands were sweating as I held the chassis of my LIVE homebrew 6146 transmitter and stuck my fingers into the tank circuit to neutralize the finals with my other hand.  I was overconfident and careless after a run of no shocks for months. It was a set up, the perfect storm, for disaster.

Suddenly, 800 volts DC erupted through my chest. I couldn't let go with my hands. I was paralyzed from the waist up. The pain was intense through my arms. It was like holding a crazy pulsating bull intent on killing me.  My legs still worked, so I instinctively stood up and ran backwards. The cables connected to the transmitter yanked the rig out of my hands. It hit the floor and so did I.  I would estimate I got a two and a half second blast. That is a long time.

I was in shock and stunned as I lay on the floor. I was still conscious and looked at my hands. The right hand had a small snakebite-type  mark.  But the left hand (the one that held onto the chassis) had DEEP torn-open flesh that appeared to be 3rd degree burns. There was no blood, just cauterized flesh.  The room smelled like cooked meat.

I stood up as soon as I could to see how badly I was hurt and was surprised to see I could keep my balance.

It took months for the wounds to heal because they kept getting infected. I really should have had stitches. I remember my girlfriend looking at my ripped up left hand and almost puking. It was a mess for a long time. I still have scars, both physically and mentally.

I've seen this pattern in many ways, in many people. Sometimes it takes an event like this to make us safety conscious. It can happen in different ways, in many hobbies and professions. Carelessness and overconfidence..

Bottom line is I haven't had a serious HV mishap since.  It was probably the best thong that could have happened to me at that time - to break the careless path that eventually led to working on four thousand volt rigs.

Even 600V can kill us with no problem under the right conditions...  even less if we can't let go.  It pays to learn on low voltage stuff. Probability says most of us will get banged at one time or another. It is inevitable and part of the learning process..  The question is how much voltage bit us and how much current flowed through our heart before we smartened up?

Actually, I am amazed that there are not more ham fatalities considering that most of us start on this HV journey without formal training. Most learn by trial and error on our own. I did. We are a lucky and smart lot, I guess.

More stories?

Tom, K1JJ

[w1vtp]

All:  part of my Raytheon safety training teaches that anything over 50 volts can kill under the right conditions.

Al

[KB2WIG]

When I was a young JayeN, I knew that the narrow slot had the juice, and the wide slot didn't.  So when I wired up the power supply for the grid dip meter, I naturally switched the 'Hot" side, and used the center, grounded part of the terminal strip for the Neutral.

Look in a late 60's handbook, and you can find the schismatic (FWIW, I never did get the thing to work FB). I wasn't too understanding of knob-and-tube wiring.  And that the outlet only had 2 slots.  And that sometimes, you forget. And please don't ground the neutral to yer dipper project.    That did really, really hurt.


klc

[W9ZSL]

Then there are RF burns.  Nasty!  Back in the 60's I got one from a Viking Ranger.  There was only 45 to 50 watts out at most but it left me with a fried burn the size of a pencil eraser on the tip of my finger.  Hurt like hell for several weeks.  You don't even have to be grounded because the rig thinks you're an antenna!

[w1vtp]

Then there are RF burns.  Nasty!  Back in the 60's I got one from a Viking Ranger.  There was only 45 to 50 watts out at most but it left me with a fried burn the size of a pencil eraser on the tip of my finger.  Hurt like hell for several weeks.  You don't even have to be grounded because the rig thinks you're an antenna!

Yep!  Got my only RF burn from a 7 watt 6V6 oscillator.  Somehow, I got my finger on the stator  of the tuning cap and ZAP. A lesson I remember to this day.  

Not too long after that, I operated an Eldico TR1 with a 1500 HV PS.  Nary a problem with that.  My mentor, Don, W1GAZ stopped by and during a quick course on operating it, drew a 4" arc off the tank with a pencil using a rubber tipped eraser. "Remember, kid, that could have been you." That made a lasting impression on me!  Note all the exposed opportunities for a 16 year old kid to have some excitement on that transmitter.

I've attached some pics of the rigs I survived  

Al

[Steve - K4HX]

450 to 750 volts. Those can kill you or at the least give you a good dose of pain. Years ago I was messing around with either a Ranger or an Eico 720 (the TX had a single 6146). The cabinet was off. It was late at night and I was tired. I should never have been working on any radio, let alone one with HV. I managed to accidentally bring my index finger into contact with the plate cap on the 6146 WHILE the TX was transmitting. So, not only did I get DC HV, but 40 watts of RF too. I saw a bright flash (there wasn't actually one, just my body's reaction) and I landed across the room. I immediately shut everything off and hit the sack. The next day, nearly every muscle in my body was sore. I still have a small scar/hole in the skin on my finger.

I was lucky. Be careful.

[Opcom]

Been burned by a hot 6L6 metal tube and shocked because someone had used pin 1 as a tie point for screen B+
Shocked from brushing against an 813 anode with 2000V on it.
Shocked by the audio voltage from a broken 1/4" plug on an Ampeg 100W guitar amp.
Seen sparks fly between a microphone stand and guitar strings. The musician got a better view.
Shocked by the 25KV from a big RCA shunt regulated color TV when having the chassis out on top of the chassis and the HV wired by clip leads.
Got a dose of X-band RF while servicing a 15KW ship RADAR set as the antenna came around once. I was told the modulator had been disconnected.

Those all happened in my youth. Learned about safety and have not received a shock or annoyance again.
One extra rule when more than one person is working on something is to trust but verify, as in disconnecting radar modulators.

[W3RSW]

Yeah, we've all gotten our share.  JJ, you're lucky to still be alive!  Uncle, Uncle! ..no more.
Ask any older electrician. All have been bitten countless times by 110/220 in the day. Some maybe 440. I remember some older sages that said they hot worked stuff, stood the burn on purpose , for a minute or two while working on older house wiring rather than finding out which fuse to pull ...   Yeah, all four of them for a choice.

All of us too have countless stories in the radio, RF and HV world.

Every equipment builder on this site from the all-tube era probably has been bitten. If you haven't I'd like to hear what you haven't built.

About that meter and HV dropping resistor, why worry about the wire insulation when the whole thing should be enclosed in a proper enclosure with rated terminals?

Because it just isn't.
A fully enclosed,  grounded metal enclosure, fusing, electronic GFI's etc. may be considered modern or fairly modern standards. We can surmise of infinite safeties to add to , surround with, and bury under and it still won't stop a surprise from your all too human operator.  At least we can share our experiences hoping the new JN's will absorb some, but in all likelihood it will take personal experience to initiate them markedly.

[W9ZSL]

As I recall from my Radio Shack days, according to their technical manual as little as 60 volts across the chest can kill you.

[N2DTS]

I never got it bad, a few brushes with some lower voltage stuff, but I really dislike really high voltages.
Inside my cabinets I have a grounding cable to make sure there is no voltage on things before I touch them.
I have nothing exposed, its all in cabinets and coax.

[K1JJ]

As I recall from my Radio Shack days, according to their technical manual as little as 60 volts across the chest can kill you.

From what I understand, it takes about 18 mils through the heart to kill. So 60V / .018 = 3.3K.

3.3K is a very low resistance and would require some special conditions to achieve within the human body. I measured my wet hands from hand to hand and find it is about 100K.   So,  .018 ma X 100K would require  1800V to produce 18 ma through my chest.

** BUT much is due to the random situation  ---  The variable here is that once the flesh starts to burn and conduct, its resistance goes down, just like any carbon arc situation. So what may start out at 100K  and 800V (8 ma)  will probably quickly turn into well over 18 ma once the human body starts to fry.  

Human hands, when dry can be as much as 1 meg. But sweaty hands, (conductive salt) or spots on the body that are lower resistance like behind the ears, the mouth, etc., can make it a different game.

That's why my situation with the charred flesh was so potentially dangerous. If it continued, the current flow through the chest would have probably soared.

What actually kills the heart is the heart's muscles and tendons simply tear themselves apart in convulsions. The heart is used to tiny voltages from the brain to pace it and suddenly it is slammed with X1000++ magnitudes.

Really scary stuff.

Something to watch out for:  We build something HV and we are well familiar with it at the time. As time goes by, we need to go back and work on it for servicing.  We are rusty and forget what we did in there. We take short cuts. Depending on our state of mind, this can be a risky combination.  Discipline can save us by treating every project as lethal.  

Frank / GFZ tells me how he handles it: Whenever he is looking at a high voltage situation, he sings that El Paso cowboy song to himself - "Come a little bit closer you're my kind of man, so big and so strong - come a little bit closer I'm all alone and the night is so long."
HA!!


T

[W9ZSL]

...and as I rode away I could hear her say to Jose.

[N2DTS]

Add some salt or minerals and you can get the voltage to kill very low.
Many people have been killed by 120 volts.

[KD6VXI]

40 volts at 40 mils (power supply delivered current) is what I was taught.

--Shane
KD6VXI

[W9ZSL]

Shane, I believe you're right.  I wasn't sure if it was 40 or 60.  Mike

[w1vtp]

As I recall from my Radio Shack days, according to their technical manual as little as 60 volts across the chest can kill you.

YES!!!  On a hot and pussy day coming across 60 volts MAY kill the victim.  Guess that's why Raytheon said 50 volts as a threshold for special handling of power supplies.  Any power supply capable of >50 volts had to have special covers on the rear terminals so that someone couldn't (without thinking) pick the PS up with one hand across the terminals in the rear and the other hand on the front panel (ground). Also special warning labels had to be applied to the front of the power supply. That's 50 volts across the chest, a recipe for death.  Remember, some of us may have underlying heart conditions to start with and that combination could spell death with exposure as small as 50 volts

Al

[W9ZSL]

I had a friend in high school who used to check 9 volt batteries by putting his tongue on the contacts !?  I tried it a few times.  Can't say I'd recommend it.  It left a taste like a dirty penny or dried lutefisk!

[KD6VXI]

Regardless,  HV is scary,  and to be respected.

ivremember been hit by 7kv across my thumb and forefinger.   Slight stink,  and a drop of blood.   That was it.   Wound caughterized almost instantly.   Hurt like hell for a week.   That happened in the back room of electronics class while working on a laser power supply.   HeNe,  we used repurchased laser copier power supplies.

Have been hit with 2.4 kv as well.   Someone thought it would be OK to drop a small self contained amp in my lap,  from behind.   I looked down and processed what was happening as my hand hit the plate choke.   Reflex muscles,  spasm,  whatever,  I threw it in front of me.   Luckily,  landed on a couch.   Neither myself or the amp suffered permanent damage.

At work,  I've been hit with 110, 208 and 220.  Above that,  people stop 'just turning breakers on to see which one makes this outlet turn on'  because your feeding other panels.   It is a HUGE difference being hit with 120 fed with 14 gauge and wired like a typical house (all spring loaded push in connectors)  and commercial (all 12, and at least my company requires all connections to switches and plugs to be screwed).

"house current" tickles.   The extra current delivered by commercial and industrial bites,  and holds on.

My latest project has a 4kv Peter Dahl in it.   I'm VERY respectful.

--Shane
KD6VXI