FvM:
To be more precise, there are two SCR in an antiparallel configuration, and 2 SIDACS. This arrangmentis to allow a higher discharge current.
The circuit as is posted is for ignition of gas discharge bulbs, mercury vapour, or sodiun, but is going to be modified to ignite TIG torches.
For calculation of the transients I have used the posted circuit.
The components values are:
Tt =15:300 turns, in a "C"" ferrite core 2sq cm cross section,
Ct = 0.15uF 500V
Cd = 0.33uF 500V
SIDAG ignition volts = 220V
5 uH is air core, 20-25 turns #22AWG, 25mm diameter air core
and the Xl=60 ohm refers to 60Hz.
If you need more info let me know
hanks