That Circuit is a UHF TV linear amplifier for small TV transmitters with output aroun 100-200mW. The transistor BGQ136 comes with SOT-122 case has gain of 13dB at 800MHz. So with input 100mW you get 2W output and for 200mW you get 4W.
Do not exceed that or you will start get bad distorted picture! Feed with 25 Volts/3Amps. Use Really big heatsink.