Sweep tube - pentode. Very versatile older tube, and there are plenty around. I have the circvuit diagram for a 400w input 2 x 6DQ5 linear if you are interested...  24 watts plate dissipation. Maximum cathode current was 1 amp and the plate voltage could stray up to 900v (average was about 200) so for a SSB linear these have great promise. A cheap legal limit linear... two valves for $40.. Bargain!

Check out http://www.813am.qsl.br/artigos/moduladores/hileman/high_output_linear_amplifier_cq_set_61.pdf