- Being that the K3 doesn't have a USB connection, what are you using as an audio device?
- Is that audio device selected in WSJT-X? (hopefully a different device is selected as default in Win-10, or system sounds are turned off)
- Is the level control on the right hand side of the main WSJT-X window possibly all the way down?
- Can you plug a headphone/speaker into the speaker jack and hear any tones when WSJT-X is transmitting?, if so ...
- Does the ALC indicator on the K3 show any bars?