[Elecraft] K3 and Alpha 91b

[n9qr at aol.com]

I have an Alpha 91b hooked to the K3 (SN 8376) and I'm having an "Odd"  
problem ... on 75/80 meter SSB, if I run the amp at 45 watts, which is what  
works on CW without issue, I encounter significant nuisance tripping of the  
Amplifier to the fault condition.  The amp also exhibits a power spike into  
the 2KW range often times when it faults.  If I reduce the  power to 30 
watts on the K3, the amp runs 1500 watts OK without tripping.   Please .... 
resist the temptation to say "Run at 30 watts then".  All  other bands ... 
except 6 meters which I didn't check, do not exhibit this  issue.  Power out from 
the K3 is 45 watts and the amp runs  1500 watts  out with NO nuisance 
tripping.  I've talked to the tech's at Alpha and at  least one other K3 owner 
has had this same problem.  He asked me to check  the amp with another radio 
so, using my spare radio, Yaesu FT-450, to drive  the amp I have no nuisance 
tripping on any band while running 45-50 watts into  the amp.  Neither radio 
has ALC hooked up, only the TR relay.  Both  radios and amp are grounded to 
the same ground buss.  RF calibration was  done when the radio was 
assembled and I have not re-done that process.
 
Any ideas as to why the radio would exhibit a tendency to over drive the  
amp just on 75/80 meters?
 
Mike N9QR