[Elecraft] RE :KPA100 upgrade and KAT100 problem

[John Huffman]

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
> 
>