[Elecraft] KPA100 D16/D17 still blowing

[Don Wilhelm]

Bill,

That is not normal - BUT -
Before I can offer a single suggestion, can you say whether your KPA100 
is the older T/R switch design or is it a KPA100 that shipped after Nov 
2006?  If it is the older design, has it been updated with the 
KPA100UPKT - and if it has been updated, was C31 also changed to 0.22 uf?

*If* you have the older T/R switch design, there is a possibility of a 
parasitic that can show up during tuning, particularly on 40 meters.  
With the new design, *if* C31 was not changed to 0.22 uf, there is a 
possibility of a low frequency oscillation that shows up when operating 
on 160 or 80 and sometimes on 40 meters.  It might be possible for an 
oscillation to create a sufficiently high RF voltage to zap the diodes 
during a tuning cycle of the KAT100.  (Note that there are many 'ifs' 
here, thus the reason for the questions to be answered - it depends on 
the level of your KPA100).

If your KPA100 is the older design, I suggest the KPA100UPKT may cure 
the diode zapping, but if you already have the update (including the new 
C31), then there is some other problem.

73,
Don W3FPR

Bill Carpenter wrote:
> Hi all,
>
> Since adding a KAT100 to my K2/100 about a month ago D16 and D17 in 
> the KPA100 have blown 3 times.  The first time I thought it was caused 
> by antenna static buildup during a blizzard but the last 2 times it 
> happened as the tuner was attempting to tune an antenna.  Could there 
> be problem with the tuner that is causing this?  Everything is well 
> grounded and the antennas are not bedsprings but a G5RV and twin sloper.
>
> I'm getting real tired of replacing those diodes!
>
> 73,
>
> Bill NZ0T
>