[Elecraft] Another KPA-100 problem

[Don Wilhelm]

Phil,

It sounds like you may have the 160/80 meter low frequency oscillation
problem in your KPA100.

What is the vintage of this KPA100?  Specifically, does it have the 1K ohm
resistor across RFC3?  That change was intended to attack a problem with a
low frequency oscillation on 160 and 80 meters.  The other part of the same
change was to decrease the value of R4 to 39k (from 100k) to raise the high
voltage fed to the T/R switch. If your KPA100 does not have these changes,
consider putting them on and then check 160 and 80 meters again.

If this KPA100 is one of the first, then putting the KPA100 upgrade kit on
it may help.  If your KPA100 has the C82 position populated and a resistor
at R23 rather than a jumper, it has not been upgraded.

73,
Don W3FPR


> -----Original Message-----
>
> I worked through the intermittent problem I had last week.  Oddly
> enough, it
> was a defective 100k pot at R26.
>
> I have been going through the alignment procedures and everything is OK
> until I am finishing up the transmit tests and check signal quality on all
> the bands.  All is OK, except on 80 meters.  On 80M both the CW
> note and SSB
> signal is raspy in the monitor receiver (a TS440 sitting on the bench).
> Power output and all else seems OK on 80M, but the sound is
> rough.  Looking
> at the schematic, I note that 80M has its own LPF path, but I would think
> the power output would be off if something is wrong there.
>
> Any suggestions of where to look?  Thank you.
>
> 73,
>
> Phil Shepard
> NS7P
>