There are a lot of cheap capacitive discharge welders on ebay
https://www.ebay.com.au/itm/Pulse-Sp...oAAOSwi8VZU2Rr
I think these will take a bit of learning to use because its all very basic and manual. There are more expensive ones like orion, where you look through a microscope and it "blinks" for you, plus it retracts the needle so you just touch the piece and pull the trigger. The charge is controlled by a computer so you have less learning with the orion.
With the cheap ones, you have to hold the piece about 0.5~1mm away and press the trigger and the needle stays put. Also, you need to close your eyes. My $300 welding helmet is too slow to cut out the flash (Its a newish well speced helmet and I don't think its faulty and works great with normal welding), but I wear it anyway to filter the IR and UV. If anyone is looking at these, I wouldn't go for one with the yellow TIG torch, which costs more. The torch is micky mouse and has no means of fitting argon to it without modifying. I've bought connectors and stuff to allow me to use my standard TIG torch, but haven't tried it yet. Without argon, things do get oxidation but it does weld.
Anyway, I was wondering if there are any jewellers here that use these (more probably the orion one) that could tell me if its possible to use this with gold solder to repair a deep scratch in gold fill? Also, could you spot weld all round a bit of wear on an edge using the gold solder to build up new gold fill and polish it flat as a repair? The gold solder is quite expensive so I thought I'd ask before trying to experiment with this. I know this isn't soldering, but they seem to call the gold wire, gold solder.