[Elecraft] [K2] ALC and power control on 40m SSB in K2/100

[Don Wilhelm]

  John,

At this point, check the audio drive and the SSBA menu parameter - which 
should be at 1 for the MH2 (or other electret microphone).  SSBA = 2 and 
SSBA = 3 are both the same and are normally not used with these microphones.

If you have any audio preamplifier installed, remove it for use with 
that microphone, they have sufficient audio.

Before drawing conclusions, set the K2 to 20 meters and see how may ALC 
bars are produced.  Check 10 meters too.  1 to 2 bars is sufficient for 
the K2.
If you obtain more ALC bars than 1 or 2 on 10 meters, then you have too 
much audio into the KSB2 board.

But if the audio drive is OK on those higher frequency bands (where the 
RF Gain is lower), you will want to check (and possibly modify) the ALC 
on the KSB2 board.

Assuming you have more than enough ALC bars on 20 through 10 meters, 
make one more check - with SSBA set to 1, check the voltage at KSB2 U1 
pin 10 (it should be near zero), and check the value and soldering of 
KSB2 R14 and R15.

Then check the soldering of KSB2 D2, R9 (10k), Q1, R4 (56k) and C38.

If all the above is correct and the overdrive condition persists, then 
change R9 to 15k (yes, I saw mention of 1.5k in this thread, but that is 
incorrect), and cut the trace on the top of the board between P1 pin 6 
and the base of Q1 and add a 1k resistor across the cut.  That should 
tame things.  You can also pat yourself on the back, pleased that your 
K2 RF chain has more gain than usual - due not only to component 
tolerances, but also due to care during construction.

73,
Don W3FPR

On 11/9/2010 4:42 AM, zendoc at netspace.net.au wrote:
> Don,
>
> The KPA100 is new -from Elecraft in September 2010 - and it therefore is the new
> design with the blue toroids @L16/RFC1.  The shield is installed as instructed,
> using the 2 solder lugs to the SO-239 socket.
>
> I took the KPA100 off the top of the rig, as you suggested, but there is no
> difference in SSB mode running into the dummy load with the KPA100 attached or
> flipped off beside the K2.
>
> Looking more systematically, I see the overdrive is most noticable on 40m, but
> is also  present on 80 and 30m.  It's not a problem on 20m and up.  Reducing
> requested power to 50W (or less) and the power out remains close to 100W on
> peaks and the ALC indicator shows 6-7+ bars in ALC mode. Seems the ALC is
> working hard but not reducing the drive sufficiently to maintain the requested
> output??
>
> Mic is the MH-2 which I run SSBA = 1,  SSBC = 2. The audio sounds very good.
> The problem reduces on the low bands with the compression setting @1:1, but then
> there is insufficient drive  for 20m and up.
>
> Does this mean my TX chain has a lot of gain on 80/40/30 - too much for the ALC
> to manage?
>