There are a few darlington transistors with an fT ratings of 20-200
MHz. IIRC, they are 2N6576, 2N6577 and 2N6578, all NPN devices with
Pd's of 120 watts. I'm not sure if 20-200 is a misprint. Looks like
one could get a lot of output with very little drive! Is anyone
familiar with the 2N657x series? Are they suitable for VHF?