[Elecraft] KPA 100 Instability

[Dale Boresz]

Mike,

Does the 'instability' occur on cw as well? If not, then it's more than 
likely NOT instability, but rather rf feedback, which in severe cases 
will sustain output, once an audio-level threshold has been overcome.

Recently, I had a similar problem. I suddenly developed a case of rf 
feedback on ssb, yet had never had it before. The only recent change to 
the shack was that I had recently put up another wire antenna, and now 
had about 4 feedlines coming into the shack (perhaps providing an 
increase in rf levels). I had talked with Gary about it and he had some 
very good suggestions, one of which was to unplug the microphone, and 
with the K2 in SSB mode, key the transmitter via the key jack. I did so, 
and didn't have any output from the KPA100. I plugged the microphone 
back in, and keyed the K2 w/ the key, again no output until I spoke into 
the microphone, and then it howled like before. Just for kicks, I 
unplugged the key from the back of the K2, used the PTT and spoke into 
the microphone, and - the problem was gone!

I concluded from this that somehow, the cable from the key jack running 
to my external keyer was picking up excessive rf and routing it into the 
K2. I plugged the key back in, pressed the PTT button, spoke into the 
microphone, and the howling was back. So, until I can address the issue 
of excessive rf, I just keep the keying line unplugged from the K2 while 
on SSB, and all works fine.

73, Dale - wa8sra



>>I recently went QRO with the KPA 100, this works great on 160, 80,  40
>>and 30 mtrs. Unfortunately on any band above this it becomes very
>>unstable within a few seconds of speaking into the 
>>microphone the
>>power meter just goes full scale.
>>    
>>