Ken Scharf wrote:
A single 4cx800 will get you close to the legal limit.

That's being over-ambitious. The manufacturer's data (Svetlana) says
that a single 4CX800A "will conservatively produce 750 watts PEP SSB,
and 750 watts Key Down CW in any of the three modes: grid-driven,
grid-driven passive input, and cathode-driven."
http://www.g8wrb.org/data/Svetlana/pdf/4CX800A.pdf

You can certainly screw more power from the tube, but intermodulation
levels will rise rapidly. When selecting a tube, a good rule of thumb is
to expect an RF output equal to the tube's anode dissipation.

If the original aim was for something "in the region of" a kilowatt, it
would be well worth considering a single 4CX800 at slightly reduced
output.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek