Its not possible to run from a lower voltage - unless I use a Variac on the input.  

A half bridge arrangement, running direct from rectified mains - so Vcc = 320V  See http://www.g4jnt.com/137tx.pdf  for teh original QST article.

Its extremally robust  - I use the soft protection system originally employed on the Decca transmitters and detailed in the write up.   It can deliver 800 Watts - thats the limit I ran it to originally, so wound back to 600 Watts it will go on forever - which is more than the ATU housing could manage!

 

Increasing the output turns ratio would do the job, but I do need an intermediate power PA, so might as well build a quickie breadboard one.   All the components needed for just about any type of circuit configuration are all in the junk box.

Andy
www.g4jnt.com