[Elecraft] Tx distortion

[Don Wilhelm]

Mike,

It may not be the KSB2 board after all.  It could be a problem with the 
base K2 PA stage.

With the KPA100 fully removed, what is the maximum power output?  Also, 
what is the DC voltage during transmit as measured by the K2 meter (tap 
DISPLAY to see the voltage), then transmit.
A higher voltage will keep the IMD low.  Use no lower than 12 volts for 
best results, 13.8 is preferred.

Do a TUNE and measure the DC voltage on the base of either Q7 or Q8.  If 
it is outside the range of 0.60 to 0.64 volts, there is a problem.  Also 
note that there is a /CLASS AB signal that also affects bias for SSB. 
Go to transmit (not TUNE) in SSB and make certain pin 6 of RF Board U1 
goes to zero.

73,
Don W3FPR

On 2/2/2019 3:28 PM, mustang65 wrote:
> Thanks for answers.
> The symetrix output impedance is 200 ohm and it is recommended to not load
> it
> lower then 600 ohms.
> I lifted the plus side of c20 and  connected a 10k resistor to ground.
> I connected the signal from the symetrix output to the plus side of c20.
> This way the signal comes direct to ne602 and u3 is not involved.
> 
> The distortion is still the same and no difference what signallevel
> I put out from the symetrix. from a very low level until a 3 bars of
> alc reading. I am still listening to the Lf signal from the symetrix just to
> be shure
> it is no clipping from the unit.
> 
> I know this is not the way to drive the k2 just trying to find a way to see
> if U3 is the problem.
> 
> The microphone I drive the symetrix is a shure sm58 and I also
> use a icom hm12 that i put direct in to the K2.
> The first 6 years I  used the Icom microphone then  the last 8
> years I used the symetrix and Shure sm58 that improved the audio.
> 
> 73 Mike sm3xgm