[Elecraft] K2 SSB ALC Problem

[Don Wilhelm]

Sanjin,

You may have some problem with the K2 VRFDET circuit - make certain the 
power displayed by the K2 during a TUNE is close to the actual power 
being developed.  Do that both with the base K2 (no KPA100 physically 
attached), and with the KPA100 attached.
If the actual power from the KPA100 does not match the power displayed, 
you should balance and calibrate the wattmeter in the KPA100.

Given that your symptoms indicate that there is too much audio drive to 
the KSB2 board, and also the fact that you bought this K2 used, look 
carefully for something like a microphone preamplifier in the K2.  One 
easy way to tell if there is anything in the mic input path is to check 
continuity between the AF Pin on the mic connector (pin 1 for Elecraft 
microphones) and pin 5 of P1 on top of the KSB2 board.  If there is not 
direct continuity there, someone has put something in the path.
Also check the value of R14 (1k) and R15 (180 ohms) on the bottom of the 
KSB2 board.

Stretching my mind for some other things - Do you have some source of 
low frequency rumble in your hamshack?  That low frequency audio could 
be picked up by the microphone, and overwhelm the audio input.  You 
might change C34 to 0.47 uF and C32 to a capacitor in the 0.0033 to 
0.005 uF range to reduce the low frequency audio.  Many have made that 
change and are quite pleased with it (I am one of those).

With the KPA100 attached, how long does it take the power to settle down 
to 20 watts during a TUNE.  It should take 30 seconds to a minute.  If 
it settles faster than that, look on the bottom of the RF Board for the 
values of R98 and R99.  If vastly different than the standard 270 ohms, 
change them back until you have this problem under control.  You may 
want to optimize the value later after this problem is solved. (these 
resistors normally have nothing to do with your problem, but if they are 
way off the optimum value for your K2, strange things can happen).

I certainly wish you had an oscilloscope.  Is there any chance that you 
can borrow one?

73,
Don W3FPR

Sanjin Tajic, E71DX wrote:
> Hello Don, hello Peter, 
>
> I tried the mod suggested by Peter but it did not really help. It seems to
> me that the ALC action is now somewhat better without the KPA100 attached
> but I am still not really sure about that - will check again.
>
> Don do you have any other suggestions what I could try to do?
>
> Thanks for the help,
>
> Sanjin
> E71DX
>