Radioshack 'lytic or whatever parts I had on hand. I tired bypassing the Radioshack parts with small sized boutique caps, but I didn't like the sound. Eventually I went back to getting rid of the caps and let the play full range with the Rag. With tube amps, I preferred the caps in.I'm a really bad person to ask about caps. Yes, they make a difference, but I don't have the time and would rather spend the time trying out different designs.