[Mondial]

You can try changing the value of the cathode resistor to improve the modulation quality. This will effectively change the grid bias and locate the operating point of the tube on a more linear part of the curve. This graph is for the 6BE6, but the 6SA7 is very similar

[Image: http://www.wa2ise.com/radios/6be6g3.jpg]


I read somewhere that changing the resistor from 1 K to 500 ohms results in improved audio, or you can substitute a 1K pot and adjust for best output and quality.

This site goes into a lot of detail on the basic circuit and how it can be improved with negative feedback, etc.

http://www.wa2ise.com/radios/amxmit.html