[Elecraft] RE :KPA100 upgrade and KAT100 problem

[Ron Willcocks]

Hi John,
              Your problem is a mirror image I had with an upgrade here a 
while ago.
On 80 and 160m bands the tuner would NOT tune 160 and 80m bands ...even 
into a Dummy load. It would go through a TUNE cycle...report a 9.9:1 SWR 
and lock into transmit. ( and not on a "in band" frequency)
I eventually found ( after being told to "think outside the square) that 
caps C80 and C81 in the KPA100 had been installed with .047uf caps instead 
of the 0.1uf they were supposed to have.
Fixing that made the amplifier stable when attached to a resonant antenna, 
but I still had trouble with it not tuning and locking up in TUNE when 
attached to the KAT100 ( but once again only on 80 and 160m) .....I 
subsequently found that the parasitic oscillation had destroyed the SWR 
bridge diodes in the KAT100...even though I had checked them earlier as 
being OK.  Changing them and rechecking the balance of the bridge 
completely cured my problem.
So.....the main problem was in the input of the amplifier causing it to 
oscillate , and it in turn damaged the KAT100. The alteration to "REV" D in 
the amplifier made the problem of wrong componentry show itself .......so I 
would be checking the input area of your KPA100....and double checking the 
bridge diodes in the KAT100 when you find it.
There is actually nothing wrong with the modifications. I have altered 5 
K2/100s here now and only been stung by that one with a prior component 
misplacement.
Hope this helps?
73............Ron ZL1TW


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