[TenTec] Power Power Power - revisited..

[AC5E@aol.com]

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