OK!! EVERYBODY!!

Step back a minute and have a look at what is being discussed he

a) This is a TUBE-based spot welder designed probably more than 60 years ago.
b) The bean counters (a scourge even then) would NEVER have specified photo-flash capacitors when just a bit more of conventional capacitance would address 'slow chemistry' at a fraction of the cost.
c) A healthy gap on the transformer would eliminate sateuration issues in this application - 'at no additional cost' and without complications, and entirely permanently.
d) This is a piece of industrial equipment designed to be used by production worker who very likely have neither the time nor the inclination to do anything other than follow directions, set the various knobs and switches then GO for hours at a time.
e) And, as with any decent tool from any decent manufacturer, it is designed to be serviced in a simple and straightforward manner by techs who need do no more than follow directions from a standard troubleshooting schedule.
f) And, finally on this list, replacement parts, especially generics (capacitors, tubes) will be entirely conventional - no silliness about "matched pairs" for instance, or boutique caps. If one has a small machine shop in Bucksnort, Tennessee ( https://en.wikipedia.org/wiki/Bucksnort,_Tennessee ) one does not have the time to search down something exotic. One is going to get on the phone to Graybar and order whatever it says on the can, and Graybar will have it in stock. http://www.graybar.com/ And, back in the day Graybar stocked industrial tubes as well.

Meaning that there is NOTHING esoteric about this device, and it will not require ANY special 'stuff' to make it go. The caps in this device are toast. If even one of them "rattles" then all of them, being of similar age, living in similar environments and doing similar work, are also done. Not replacing all of them is just plain stupid. Full Stop.

Purchase physically rugged caps that either are, or add up to, 200uF & 450 VDC per each, at least. Make sure that the soldering points and connections can handle anticipated voltages and currents. Replace all the tubes, even if they are not necessarily done, as now you will be starting fresh, nor is the investment all that much. If I have 2D21s, I would send the whole shebang to Oregon/Washington State for US$30 including shipping and think I was making too much. Otherwise, AES will do the same for perhaps half-again as much.

Sheesh, guys and gals - it is almost as if this were rocket science. It ain't nohow.

Peter Wieck
Melrose Park, PA