The Power Amplifier Build – Prologue, Part 1
The Power Amplifier Build – Prologue, Part 1 Big Tubes, Tank Circuits and Design Philosophy This project started brewing back in 2019 (actually, even before that), and by 2020 I had begun collecting the last pieces and putting the plan together. I had previously built an amplifier using 813s, but I wanted to take things up a notch — both in terms of scale and concept. One of the builds that really caught my eye was from EX8A. Although my final design diverges significantly from his, his approach showed a lot of clever problem-solving. In particular, his plate choke switching network intrigued me. Clarifying EX8A's Choke Design EX8A uses a conventional DC feed with the plate choke placed directly at the tube anodes. What makes his approach interesting is the use of relays to switch different segments of the plate choke. This, in combination with a bypass capacitor and the tubes' internal capacitance, creates a parallel resonant circuit. The purpose is twofold: To avoid destruc...