Monday, July 19, 2010

KT44 push-pull valve "quality amplifier"

Here's the latest of my Wireless World Quality Amplifier builds. Again I've avoided the expense of vintage PX4 or PX25 triodes and used tetrodes. This time however they are strapped as triodes as in the classic Williamson and Leak TL/12. Those amplifiers used a pair of Marconi KT66 beam tetrodes as triodes. Williamson reckoned the characteristics of these valves when strapped as triodes was equivalent to the PX25. I've chosen to use the less common, but now far cheaper KT44 - actually Mazda 11E3, but they're the same valve. The KT44 is a rather different looking valve, it looks more like an 807 - itself a variant of the popular American 6L6G valve, much loved by electric guitar players.

From Quality Amplifier
The circuit is very simple. In essence it is the output valves and drivers from the Williamson, with the phase-splitter and feedback loop removed. So at present there is no negative-feedback, as in the original 1934 Wireless World Quality Amplifier.