[Elecraft] KPA100 D16/D17 still blowing

[Bill Carpenter]

My amp is the older design shipped in August, 2006 but the KPA100UPKT was 
installed.  If the new C31 was part of that kit it's in there but if not I 
don't think it is.  Question - would it make sense to tune at low power 
until I figure out the problem?  I'm thinking that would avoid blowing the 
diodes and still allow me to use my new KAT100.
----- Original Message ----- 
From: "Don Wilhelm" <w3fpr at embarqmail.com>
To: "Bill Carpenter" <nz0t at cox.net>
Cc: "elecraft list" <elecraft at mailman.qth.net>
Sent: Monday, January 07, 2008 8:19 PM
Subject: Re: [Elecraft] KPA100 D16/D17 still blowing


> 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
>>
>