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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