[Elecraft] K1 AF sidetone loudness problem ?

[Mike Morrow]

Roland_DF1OE wrote:

> Last Year i built my k1 #3310...

Excellent choice!

> I ve a little problem - may be it is quite normal...

What you describe below is very abnormal. 

> during sending cw the sidetone is very very loud - louder as it is during
> adjusting  ST_L and much louder than testing it with no cw HF transmission.
>
> During transmission it gets louder after a time. Even if i put ST_L to 1
> (one) i get a loud sidetone during cw hf transmission.

My first guess would be some disturbance at front panel board FP-U2,
the DAC which actually produces the sidetone.  The DAC uses Vdd from
the 6.0 vdc regulator FP-U4 as its reference voltage.  Perhaps you
have some RF intrusion or regulator load change during transmission
that is upsetting the regulated Vdd at pin 7 of FP-U2 that is coming
from regulator FP-U4. 

Such regulators can become unstable if there is not a small capacitor
on the output, although the ZR78L06 is not supposed to need one.
Regardless, the FP board has such a capacitor (FP-C5, 0.01 uuF) mounted
on the "bottom" (back or rear) side of the FP board.  I would check
that it is in place, and properly soldered.

FWIW, here's the MAX518 data sheet:

 http://datasheets.maximintegrated.com/en/ds/MAX517-MAX519.pdf

Of course, perhaps it is something completely unrelated.  But it is
definitely abnormal.  This is what I'd check first.

73,
Mike / KK5F