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Old 17th November 2008, 10:39 PM   #1
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Default Top cap tubes+ arc welder

While working in the metals shop today, I started wondering what would happen if I connected the electrode holder to the top cap of a tube and the ground connection to the cathode. I'm guessing it wll melt in a matter of seconds? Anyway, just wanted to get your opinions before I try it.
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Old 17th November 2008, 10:50 PM   #2
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I suggest you send Tubelab a message, he has extensive experience in these matters.
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Old 17th November 2008, 11:35 PM   #3
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Default ummm - I'm guessing nothing.

arc welder at around 100V open circuit - not enough to strike an arc in the valve...
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Old 18th November 2008, 12:14 AM   #4
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YEah, I thought about that... so maybe I'll just break the envelope first to allow some air in to ionize
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Old 18th November 2008, 02:57 AM   #5
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Quote:
I suggest you send Tubelab a message, he has extensive experience in these matters.
OK, I have hooked tubes up to a lot of things but not an arc welder. Only because I don't have an arc welder! As previously explained an arc welder puts out about 50 to 80 volts. This is within the normal operating range for most tubes. Yes an arc welder can put out a whole bunch of current (amps) but if the tube doesn't draw nmuch current nothing spectacular will happen. Breaking the glass won't help either.

The only way to get some fireworks started is to apply voltage to the heater. Next the plate voltage supply needs to be current limited or else the little strap that connects the cathode to the pin will blow like a cheap fuse. This is the weak link when seriously abusing a tube. The cathode is the next thing to go.

Some of my best meltdowns involve a plate to plate plasma in a gassy tube. The plate connections are usually made with stiff heavy wire, so they don't burn out. Connect one section of a dual tube up in the normal manner (I used a 6AS7). Operate this section far above its ratings so the plate glows. Get it hot enough so that it can act like a cathode. Apply a more positive voltage to the plate of the other section and current should flow from plate to plate. Work the current and voltage just right to get both plates glowing, let it get hot and then a plasma should erupt between the plates. When the glass starts to melt it will bulge outward indicating a positive pressure inside the tube.
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