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Get familiar with the reaction system: Introducing the Reaction System
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I'm only about 20 minutes through the video. Had to pause to take care of some other junk. But that is really cool. Home brew DIY spot welder? Makes me want to experiment with spot welding my xovers together instead of soldering them.
Just finished the vid. Like watching Macgyver scratch build a vacuum tube from spare parts left behind at an abandoned warehouse. These tubes, however, will probably burn out fairly quickly, because it is impossible to completely evacuate the tube. A getter must be applied inside the tube to absorb gas, otherwise the small amount of gas left over will burn up the filament and plate in short order.
EDIT: Whoops. I just watched another one of the designer's vids, and a getter was actually used. I was looking for a shiny type silver coating on the surface of the glass. But the getter used here was 3 loops of 20ga titanium wire welded in a spiral just above the plate. My bad.
Could you evacuate the air from them with Helium and then seal the bottom? Or does it have to be an absolute vacuum to work properly? I've not dove into tube tech enough to know. Up-ending a test tube with Helium rising into the tube via water barrier can evacuate the air. Then remove the tube from the water and since the Helium is lighter than air it keeps the air out. I did this in a lab back in middle school.
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It needs to be a complete vacuum. The designer here was using a vacuum pump to pull as much air out as possible through a glass evacuation tube. With the vacuum pump running, the evacuation tube was heated up with a torch, twisted, and sealed off. But there would still be a little gas left over. The getter then chemically burns up the remaining gas.