I've had a few attempts in the past of building a class E amp, but never quite got the right results.
I dug out an old board where I tried to replicate the NS-40 and decided to try a different drive circuit. I took out the oscillator and drive circuitry and replaced it with a NCP81074A gate driver.
It somewhat worked - I was able to get some power out. But it isn't as efficient as it should be because the gate drive is ugly. Need to look into it more.
The circuit
The ugly gate drive
