C1,C3 = 75-380 pF mica trimmer, ARCO 465
C4-C8 = .01 uF 1 kV disc ceramic
C9,C10 = .1 uF 500V disc ceramic
L1 = 6 uH. 25t #24 ga.enam. 0.5" dia.
L2 = 210 nH. 4t #8 ga. .75" id, 1" long
L4 = 2t #20 PTFE on .5" ferrite bead m=850
Q1 = APT ARF448A
R1 = 25W 5W non-inductive
T1 = Pri: 4t #20 PTFE, Sec: 1t brass tube on 2 hole balun bead. Fair-Rite #2843010302 m=850
High voltage MOSFETs are now available that combine the best practices from the RF world with the economy of the switchmode devices and packaging. They are available in mirror image pairs and the heat spreader of the plastic TO-247 package is connected to the source.
Download the aplication note for this circuit 500W 27Mhz RF Amplifier HERE