I have one of these and it's just laying around. It's too dirty for my taste. I looked at the guts to see any obvious changes I could make. It uses tantalums and the lm13700. It uses mpsa18 transistors. A buttload of them. Would changing these transistors make any difference? Like a 2n2222 or bc109 or 2n5089? All the components look pretty good. Just a thought.
