The preamp’s key components are not easily found in modern production models. I tested numerous combinations of transformers, tubes, and coupling capacitors before deciding on the final tonal characteristics that sounded best to me.
Matched pairs of 1960s new-old-stock General Electric tubes meet or exceed published specifications of transconductance. The GE 5-Star 6072a is legendary for its larger-than-life 3D quality, while the choice of either a NOS RCA or GE 12AU7 contributes its hi-fi soundstage, tight bass, and neutral highs.
Jensen has led in transformer research for decades. Their JT115k input transformer is designed for the highest practical 1:10 step-up ratio within their company’s design tolerances. Paired with Jensen's JT-10K61-1M output, these are perfect transformers for a tube preamp.
Glass-sealed Russian paper-in-oil and Teflon bypass capacitors are used for coupling following tube gain stages. Polypropylene film and electrolytic caps are used elsewhere in the audio and PSU circuits.
High quality stepped-gain rotary switches are used instead of potentiometers for repeatable gain selection and to help maintain signal integrity.