If I hadn't been so pleased with my Quality Amplifier and turned it into my hi-fi system I would have tried out other valves and circuits.
This new amplifier will be one, or more, of those experiments I didn't do with the Quality Amplifier.
The KT44 is the 4V heater equivalent of the KT66. The base is also different, it uses the old British 7 pin base. I had one of these in my junk box, and was able to pick up a couple of others quite cheaply on Ebay. They should give characteristic not unlike the PX25. I don't intend to run them hard, so the performance will ideally be close to that of the PX4.
Driving these directly with a phase-splitter inter-valve transformer could create an amp with just 3 valves, plus rectifier. To drive them I'll use another 4V valve. An obvious choice would be a 4V triode but I also have a couple of ex BBC AC/SP3 pentodes.
I rather like the fixed bias technique used in Woodville's 1948 KT66 push-pull amplifier. These days it doesn't need a valve rectifier.
Mazda's Pen46 appears to be the same valve with a Mazda octal base.
The BBC Type A Desk http://www.btinternet.com/~roger.beckwith/bh/typea/typea1.htm
PX25 data sheet, includes simple push-pull circuit http://vip.cyberexpress.net.hk/~leekc/database/px25.pdf