[Sean Williams]

Yes, GT1C is certainly a valve it uses.

I think the project had loads of these - Billington sorted huge boxes of valves out for Colossus.

Still, I will have a rummage and see if I can spare any for them.

The comment on Powerhouse regarding the harvesting of old exchange equipment is indeed correct - tons of it was rescued by local BT engineers, and sent to Bletchley.