The symptom is output power only half of its original capability.
Tracing the RF signal from pre-driver output has shown that the pre-driver (2SC1969) is working normally.
The driver consists of pair of 2SC3133. The signal output from the driver is somewhat distorted and lead to hypothesis that the driver is not working properly.
It is found that only one driver that did not provide proper gain and causing the output signal shape to be non linear.
After replacing the driver, the output can go as high as 150W.
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