Hello,
I'm building a jocabs ladder. I have torn a tv apart already to get the transformer out of it, 26.4kv . Should I leave the transformer on the tv board, cut and tape off all the old wires off or completely remove the transformer? I''ll prolly end up looking for some 14-10 gauge wire to use and have random 2x4s floating around that I can use for bases.

Any thoughts or suggestions?
thanx
BobJoe

http://www.kronjaeger.com/hv/hv/exp/jacob/pt1_l.jpg

 

Does anyone know where the voltage ground is? Or where one could get the general schematics of an RCA tv board?

 

Most "Line Output Transformers LOP" (flyback transformers...FBT) out of any TV less than 15 years old or so, are of a Diode Split style, meaning there are built in diodes in the EHT winding, so the EHT output is around 28 - 30KV DC (as required by the Anode of the TV tube).
Older style TV's that used a separate "Tripler" unit to rectify and step up the voltage from the LOPtx dont use the built in diodes, so the output is normally around 8KV AC.
One side of the EHT winding is obviously the large rubber "Aquadag" connector, while the other is normally labled ABL.
The input winding normally has one end at the supply rail (112 to 140 volts depending on design) and the other end goes to the collector of a high power switching transistor working at the Horizontal frequency (15.625 kHz for PAL)... this is obviously going to be around the best frequency to use as it's what the transformer is designed for. A lower voltage could be used by winding your own turns on the transformer.... normally the turns ratio is less than one turn per volt. Needless to say, the voltages generated could be potentually lethal, and at the very least will cause a muscle reaction that will embed a screwdriver into the wall from 10 feet..(believe me).

A picture is worth a thousand words....

 

Does anyone know where the voltage ground is? Or where one could get the general schematics of an RCA tv board?

What model?

 

Hey:
the weird this is that schematic almost makes sense to me, not completely but... is the model written on the board or will i need to dig the tube out of the garbage?

thanx for the warning of the high voltage being lethal. i was aware of that, but still need to get the burried into my head. im thinking about getting some plexy glass and making a case around the ladder so no one accidentally touches it after its completed.

thanx so far and ill try and find that model info
BobJoe

 

Hi,

Shielding around a Jacob's ladder is always a good idea. Not only do you not get zapped, but stray breezes don't blow out the arc and ruin the effect. Check out the movie "Frankenstein" or "Young Frankenstein" (uses the props from the original) to see how it was done.

Sparks transmit energy all over the RF spectrum. You could get to be real unpopular if yours kills wireless phone and cell reception. Broadcast radio will also get affected. Invite the neighbors to see the show and don't run it all evening.

 

hey,
Thankx for the heads up on the RF thing, I was unaware of that.

Anyways, everything is under loads of garbage other than the board and that says it's a 3400 area keyboard, I think thats the info for it?

BobJoe

 

I don't know if you know this already, but the transformer in the TV is a flyback transformer. It's controlled by the TV's flyback circuitry, and will not work without it.
http://en.wikipedia.org/wiki/Flyback_transformer

 

You can use a flyback in apps such as this, with some simple mods, check out this link:

http://www.aaroncake.net/circuits/hvgen.htm

Also, this link: http://www.angelfire.com/80s/sixmhz/flyback.html

A google search will turn up multitudes of drivers and simple mods for use with flybacks..... Great small HV source. Now if you really want to have fun, go to your local neon sign company and buy an old used neon sign transformer (The large ones, not the small dinky ones) for about $50.00! Those make a fun Jacobs ladder. I'll take some pics and post them when I pull it out for Halloween!

 

OH sweet!!! I can't wait to see pictures of your Jaboc's ladder.

I still have to look into this flyback thing. Then I'll have to figure something out.

I don't think anyone seriously believes that I plan on having this fully built and going.

 

Hey,
I got the thing built and put together but everytime i turn it on i get one spark and then a relay shut it down till it cools?/resets and then it repeats. how do i convince that relay that it is not shorting out and is ok?
BobJoe

 

You don't. If its getting too hot, then its getting too hot. You need to reduce the current in the arc. Try putting a ballast on the input, or using an autotransformer. Try a current limiting resistor between the HV and the arc.

And please be careful with this thing. Its niether a toy, nor a Halloween decoration. A buddy of mine did time in the state penitentiary after his 4-year-old son was killed by a home-built jacobs ladder.

 

will a resistor handle 26.9kv though? i would suggest another transformer to increase the voltage more and drop the current but i dont think that is feasable.

im sorry to here that, i think the loose would be far worse than the time. right now since we dont have a case for it yet my dad (with his great trust in my work) has a fire extinguisher, and with the same faith as my dad im using a wooden broom handle to turn it on.

 

I've seen resistors rated for as much as 50kv. You should be able to find one on the internet. The ballast or variac on the input is probably an easier way to go.

It is the current coming out of your hv supply that needs to be limited. Overcurrent condition there is what's tripping your protective device.

Its good to know that you are taking safety precautions. The fire extinguisher that you have is "Class C" is it not? "Class C" extinguishers use non-conductive chemical to put the fire out. They are approved for use on electrical fires.

 

not sure what class it is but we have 2 in the garage so im pretty sure my dad is using a class c because he looked at each one before he took one.

 

It's no less of a toy then a computer, or any of the other electronics gadgets we let our children play with these days...The issue is safety and responsibility. I'm not trying to argue with you about the dangers of HV, but lower voltages can be just as lethal. See the safety section on allaboutcircuits.

My jacobs ladder is all enclosed, and the ladder is surronded by a plexiglass "square" all the way up, so you can see and enjoy the show, but there is no way to come in contact with any electrical component without tearing apart the whole ladder, with tools. (or a large hammer, I guess...) No part except a switch is exposed, and it switches standard household voltage, and poses no more danger then your ordinary light switch.

You will often see jacobs ladders in childrens science museums, they are fun! Yes, be carefull. That should be a given. Don't just leave the ladder out in the open where a little kid, or adult, could grap it!

So I guess what I am saying is, YES, BE EXTREMELY SAFE AND CAUTIOUS, but at the same time, HAVE FUN! That's why I am going into the electronics fields, it's fun, I enjoy it, and I can easily see myself working in it until I retire and still enjoying it. That's what it's all about, IMHO.

EDIT:
I'm not saying let your kids "play" with a jacobs ladder, but a properly built one does make a fine Halloween decoration!!!

 

I've recently aquired a Franceformer 15kV 60mA neon sign tansformer and made a crude ladder that's shooting a flame about 7" at the top. I've got some new/better/showier materials to make the risers, but i'm curious about some more asthetic things.

First order of buisness is what material should I use to build the case for the transformer? Wood is easy to work with (though flamable), but I'd like to entertain other suggestions. Also, where could I find feedthrough porceline insulators for HV like these but not in bulk. I need 2, not 50

Also, I'd love to mount some analog dial gauges for shear geek appeal I'm thinking a voltmeter and an ammeter. Anyone have a case mountable 20kV dial and 100 mA dial source?

Of course, I'll build a glass or acrylic case around the top. I'm also thinking of closing all case doors with electromagnets so that no one can open it if it's plugged in.

 

hey
i was able to cox my ladder to jump to life today. i havent been able to get it to do more than a spark, then the relay goes. today i was poking around with it and after i cut the casing that held the two wires side by side and playing with the antenas a bit i was about to get about an inch to go up it rather quickly up about 4 inches up, from about 1/4-1/2 inch up to a max width of about 2? inches. it was fast time wise, maybe a couple hundredths of a second long. really kewl while it lasted, but now i cant even get it to spark so i burned something out nicely. off to find an older tv tomorrow.
BobJoe

 

Wood should be fine for a transformer case, as long as a bit of ventilation is provided. Wood was used for many university-grade or museum-grade ladders. I suspect any insulating material would work - plastics, stone (if you have lapidary equipment), micarta, glass (thick), pottery...

 

hey
went out today and bought an Old tv. sheesh, talk about being build like a tank, i had sparks jumping between two glass tubes and it just keep on trucking! anyways i got it built and its working, kinda... i need to re organise the antennas because right now its having a hard time sparking, and its only making it two about 1-2 inches wide then it gets stuck there and stays at that hieght. i have an idea on how to get it to spark better at the beginning but how does one "cox" it to continue on up the ladder?
BobJoe