Hmm, sounds like a high SWR situation. With a Thunderbird, assuming proper
assembly, your actual SWR should be very low. Your 238 should be in bypass,
with the Z knob straight up and the tuner out of line. Max power out should
be 100 watts CW, and depending on your voice waveform, no more than 80 watts
or so SSB. Your
Ic meter reading should be no more than 20 amps - below the red mark on the
meter.
That said, 140 watts sounds suspicously like 100 watts of forward power,
plus 20 or more watts of relected power, plus MAYBE re-reflected power.
Now, from experience with solid state power amps going back to the early
1960's I can tell you that whether reflected power is re-reflected or not
depends on a number of imponderables.
If it arrives when the final transistors are either in full conduction or cut
off reflected RF will be rereflected and add to your power output. But if the
finals are in some state of conduction the finals will absorb relected
power. Only some - and sometimes none - of the reflected power will be
re-reflected. What's not reflected will be absorbed by the finals or the
power supply.
And it will do all sorts of strange things, from making the heat sink get
very hot very quickly, to making your finals think they are operating with
higher than normal collector voltage, to running the collector current sky
high.
So - check your SWR with the tuner out of line. If it's not low, adjust your
antenna until it is. Keep the Ic below 20 A. And remember that the indicated
power out in Tune will be your PEP regardless of what any FWD meter reads.
73 Pete Allen AC5E
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