Sometime ago I remember that J. Browsky of www.tubecad.com reviewed several OTL variants with output caps.
I have preliminary explored this one (I do not know if it fits exactly with one of the mentioned Browsky's variants).
This particular one requires one +300V HT only and the standard negative voltage for fixed bias.
To my knowledge it might be one of the simplest OTL for DIY people.
In parallel with the speaker there is a 1:1 transformer for the 6 dB differential feedback that is applied back to the driver.
The performance (see simulated output spectrum @ 650 mA peak current, with predominant third harmonic) appears better than the novel circlotron just posted. And probabily there is still room for some improvement.
Best Regards
Luca Cellai
ecc230
