It was about time to get my hands on this driver experiment. I’ve been trying to find the time for a while and could only make it due to the obliged COVID-19 isolation upon return from holidays.
The idea is simple. I wanted to use a pentode driver to swing large volts (e.g. 200Vpp) whilst retaining the triode-like characteristic from harmonic perspective and low distortion. A nice challenge and fun to work on.
Have to say that the parallel/parallel feedback (also referred to as “Schade feedback” by some in audio) when applied locally in the output stage, does sound very nice and is a very nice way of implementing high-gm pentodes used for vertical service in TV. They can produce very low distortion and sound amazing when implemented correctly. I’m not covering this now, as it has been dwelled on for some time by many good people out there.
The circuit topology is as follows:
