Additional Heat sinking (that works) is not simple and would be only be needed if there will be sustained high power operation or a particularly hot internal case environment?
The resistor (R42) that biases the series ¡®envelope¡¯ transistor (MPS751) has been changed over time in response to analysis of built units operation ?(may relate to transistor batches ) ?where it is not getting ¡¯fully on¡¯ (especially if lower supply voltages e.g. 9V are used).? So a slightly lower value ?can cut its own, and PA area, dissipation generally and allow a few more mW of max output power.? ?The value was originally 1.2K, then 1K, then? 820R and the latter certainly works better on my 9V WSPR QCX's??
Bruce Akhurst