Errrmmm....
I supplied 5 PM premium Chinese 12AX7s at only £9 each.
They reside under their can covers behind the shielding plate.
Also, the amp has had the bias adjusted to take a range of valves.
If they are new htey whould just pop in and be happy together.
SC120s have 6 valves, so nothing is overworked. I have seen them running on only 2 valves.
Pushing about 22 watts. Loud as &*%$ still. And those partridge transformers didn't care a jot.
It is only the goofy active preamp that keeps them from being boutique grade classics. And you can strip that out and replace it - or put in a bypass and run them with an outboard pre...
Cheers
Chris
PS Plenty more Sound Cities in the stack...