I would suggest you look for early model Tesla ECC803S tubes. They were a copy of the famed Telefunken ECC803S (12ZX7 equivalent). These come in a yellow box. I am not referring to the current JJ production; they are not comparable.
Due to the unit's age you should have the entire amp checked out; if capacitors are original they will almost certainly require replacement. This is a good time to upgrade the coupling capacitors, too.
While it is open you can assess the feasability of installing a detachable AC socket as well as upgrade the RCA inputs/outputs.
Be careful if you open it up; the transformers will hold a charge for quite a bit after you unplug them from the speakers and power the amp down.
Due to the unit's age you should have the entire amp checked out; if capacitors are original they will almost certainly require replacement. This is a good time to upgrade the coupling capacitors, too.
While it is open you can assess the feasability of installing a detachable AC socket as well as upgrade the RCA inputs/outputs.
Be careful if you open it up; the transformers will hold a charge for quite a bit after you unplug them from the speakers and power the amp down.