The point is if you change to components of a different type and printed circuit boards with different circuit configurations you may end up with an amplifier that sounds better, but if you fit a hybrid engine and battery set up to a Mk. 1 escort it may drive and perform better but is it a Mk 1 escort? no. QUAD 303s are antiques let's leave them as antiques. If you want a superb sounding amplifier buy one, there are plenty out there, Lets leave Quad 303s alone and show some respect for a great design that has stood the test of many years.
