Push-pull KT44 triode amplifier

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. 

Valve data

Equivalents of the KT44 are CV73 and 11E3  See http://www.r-type.org/exhib/aai0163.htm
Mazda's Pen46 appears to be the same valve with a Mazda octal base.


PX25 data sheet, includes simple push-pull circuit  http://vip.cyberexpress.net.hk/~leekc/database/px25.pdf

Michael Saunby,
17 Apr 2009, 14:47