Spot (tack) welder

Estimate reading time: 2 minutes

We can’t use a soldering inside the vacuum tube, the tin would melt during the heating of the tube because of the tin low melting point. Instead of that it is necessary to use a welding, probably the best solution is small spot welder, I choose a capacitive version. Large capacitor is charged on 16-20V and then discharged via thyristor and electrodes into the welded stuff. You can find tons of info about the spot welder, I won’t mess the internet by another one 😉 I recommend this one: Tab welder.

Just some photos of mine.. I had to add another capacitor, this one is weak, and some foot-switch..

I used 4AWG flexible copper wires, little thyristor ČKD,audio capacitor 2 farad (0.28 Farad in real..)


The black cylinder is a capacitor, I didn’t expect it to be really 2F for that price ($30).

Brass rods as electrodes, soldered on the copper core and covered with heat-shrink tube.

Tips of the electrodes.