1. Bypass your 10k cathode resistor with a 5uF cap.
2. Ditch the bright cap on the high gain volume control.
3. Replace the 470pF bypass cap on the 470k/470k network with
a 0.002uF
 
Plug in and listen to some nice meaty distortion in high gain and it'll
really wake up the low gain mode too!
 
Carl Z
http://www.zwengelamps.com