RF Transmitter Amplifer

Why do you want to increase the power output? If it is to increase range

- can you not make better use of the power you have by using more directional transmitter and receiver aerials? A couple of nice 433MHz yagis should do nicely..and will possibly be a more legal solution than the one you are suggesting.

But it is easy enough to design a linear amp that will operate at UHF. (instability/ physical layout is the biggest problem)... Just search for UHF broadband amp designs.

What range do you want? Is there anything between transmitter and receiver (eg walls)? Are there any sources of interference nearby (eg arc welders)?

Those units work at UHF. Just like lighthouses and telescopes use lenses and reflectors to make the most of the lamp power- it is possible to get "better transmission" using reflectors and directors with your radio link. That should be the first thought and not just using a more powerful transmitter. Simple reflectors at both ends will have a much greater effect than doubling the transmitter power..