Quick and Dirty Spot Welder

So a while ago I was gearing up for my first attempts at building a crude vacuum tube - a triode - in the manner described in "Instruments of Amplification," by H.P. Friedrichs. The electrodes need some form of welding for assembly - soft solder won't cut it. Rather than getting a small welding torch and teaching myself to silver solder or straight-up weld very tiny pieces of metal, I decided to build a spot welder out of parts from my Junque Pile.

Any means of passing sufficiently high current through a joint of metal such that it briefly melts and fuses will work as a spot welder. I have several power transformers from microwave ovens laying about, and so one of them seemed a likely candidate for cannibalism.

I took a hacksaw to the high voltage secondary winding while being careful to not damage the primary winding. After cutting off one side of the secondary flush with the core, the rest can be hammered out using a small piece of wood as a punch. I paralleled up four lengths of 10 gauge stranded wire and wrapped as many turns of this as would fit through the core windows previously occupied by the secondary winding. This ended up only being four turns. 

The output is fed to the work piece via any number of methods, though my favorite is a modified hot wire insulation stripper. I exchanged the original nichrome elements for thick copper and rewired it to put the copper bits in series with one another when the gap between them is bridged by something I wish to spot weld.

This image shows the incredible simplicity, and a clamp mounting for larger work pieces.