I did some more research into duplicating a pulse welder.
The central principle is to apply a pulse of low voltage high
amperage AC. This can be easily done at low cost (and great hazard)
with the help of a microwave oven step-up transformer re-purposed as
a step down.
Google "MOT-spot-welder" at Instructables.
I think I could use this by itself to fuse fine silver, but I think
I'd put a few extra things around the naked transformer if I could
for the sake of safety.
Central to this would be a bank of super capacitors connected in
series-parallel. I'd isolate the bank from the rest of the world
using a single-pole double throw switch.
On one side of the switch, I'd connect the line voltage through a
step-down transformer to a rectifying system to trickle charge the
capacitor bank at 12 volts DC.
The other side of the switch, I'd connect the 12VDC bank to an
off-the-shelf power inverter. The inverter would then create 117V
switched AC to be applied to the repurposed microwave transformer.
If I want dial-in precision for repeatability, I could replace the
single pole double pole switch with relays.
Andrew Jonathan Fine