There is a great article on Glass Audio called try Battery Tubes - Larry Lisle

Thank a lot Larry Lisle for inspiration. This artcle was possibly handed to me by someone who was working at an electronics lab at the Airport of Ellinikon when doing my military service and a good officer who apreciated my grandfather George sent me to the music department of the Airforce. We were discussing with this technician the 1H4 triode.