The Cavalli is a Hybrid amp a very pricey one. It sounds wonderful with the HE-6 headphones. However I heard that the next morning someone decided to “classify” the amp and blew out a channel. What I was trying to say that this test unit was designed with two set of sockets that can use either octals that have 6SN7 basing or novals that have 12AU7 basing. Only one set can be used at a time and the sockets are arranged in a way that you cannot put four tubes in it at once. It has 6/12v switch and a high voltage switch of 200v or 330v which is half at the tubes. Part of this is somewhat like you did with the rosgr63 amp.
Your idea of trying the 01A tube is good and the tubes are easy to get.
I have built a amp for someone in New York that is fully adjustable B+ with a pot in a adjustable regulator 150 to 350 volt