[Elecraft] RE :KPA100 upgrade and KAT100 problem

[Ron Willcocks]

Great Scott......I am worse than I thought....make that C80 and C81 in the 
second sentence ......
73 again...Ron
Hi John,
                Sorry...I had a "Senior moment" nominating C80 and 
C81......what I meant was C58 and C59 were wrong in the PA I worked on. I 
believe C89 and 81 *should* be 472's ...or are according to the latest 
release of the circuit I have  .....however....there could have been a 
change, and if the latest instructions from Elecraft dictate otherwise I 
would follow instructions.
Yes I think it is wise to fix the amp first. It might be wise to check the 
HV you get at the junction of R11 and C77 . In the amp I mentioned, the 
voltage there was falling to under 80v when the KAT100 was plugged in, so I 
went back to the 39k resistor at R4 to bring the voltage back in range.
Good luck......and sorry for my mistake....
73.....Ron ZL1TW

At 03:59 p.m. 19/11/2006 -0500, you wrote:

>Ron -
>
>I suspect the same has happened to the KAT100.  I did replace the diodes 
>and it worked for a bit, but the problems quickly returned.  Probably blew 
>up the second set of diodes.  Setting the KAT100 aside until the KPA100 
>behaves.
>
>In C80 and C81 I have caps marked "562".  The revision D manual says these 
>should be 472's, as do prior manuals.
>
>I then found the "KPA100 Cap Kit Upgrade"  which replaced C80 and C81 with 
>562's (5,600 pF).
>
>Should I go back to 472's?
>
>You use .01 uF.  Would that be better?  How did you arrive at .01 uF for 
>C80 and C81?
>
>All help greatly appreciated.
>
>73 de K1ESE
>John
>
>
>
>Ron Willcocks wrote:
>>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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