[David G4EBT]

Typical DAC90A then - C22 gone bang, C18 leaky, so UL41 overdriven and hence, OPT primary is open circuit. (Presumably your multimeter reads '1' for open circuit?). Looking on the bright side, at least you've made a start in identifying the culprits.

The retaining springs are just rings of wire with overlapping ends, so if you poke a small screwdriver or pocket knife blade between the inside of the ring and the skirt of the valveholder you can open it up enough to be able to grip the wire with pliers and open up the ring, then just slide it up over the valve. Be very careful not to damage the fragile glass pip in the slot of the valveholder skirt.

If the heaters of all of the valves are intact, you may as well wait till you've got the set working to see how the valves perform. The only way you could test the valve without a valve tester is if you've got another set which uses a UL41 in which to try this one. It's always handy to be able to substitute valves with known good ones to see if the existing ones are past their best. It's the UL41 that has to work the hardest - they're starting to get a bit expensive these days.

Good luck with it!