Make exciter 0-40W RF

I want make a pll (exciter). I have a pll, the output RF is 0.5W. Drive the BLY87A is good idea or bad?
I believe to take 5-7W (or 2SC1971,2N6080), and them to drive MRF240 or 2N6084 or BLW60 (about 40W).
In which way to make adjastable RF (0-40W). This way is right? with LM317 adj VDC in stage of BLY87A?.

It's difficult to determine what you are trying to do. I can tell you that numerous amateur radio organizations have published books, magazines, journal articles, etc on the subject. Radio Society of Great Britain (RSGB) and American Radio Relay League (ARRL) are two of the larger organizations. I recommend that you adhere to the regulations regarding operation of the transmitter/exciter or if you operate it into a dummy load that there is no accidental stray leakage.