Rik Strobbe wrote:

[...]
As the beacon is meant to be low-power (10mW and less) a relative small TX
power can be used (50 Watts and less), so it can easily be overdimensioned
to provide extra safety.

Maplin has a small class A amplifier using a LM 1875 that easily puts out 25
watts at 136 Khz. It is stable, has automatic current limiting and overheating
protection
Because it operates in class A, the output can  be controlled simply by a step
attenuator at the  _input_   of the amplifier.

Just a thought

73
Andre' N4ICK