Back in 1955, some of the big audio issues were: Which provides higher fidelity, triodes or pentodes? Feedback or no feedback? Active or passive? Solid core or stranded wire? Does this all sound familiar? It was in this climate that D.T. Williamson's amp arrived. The old guard believed that there was no substitute for 2A3s push-pull. But the hot issue in the audio mags was high power. High power back then was only 20-30 Watts, but it was thought that the extra headroom contributed to a sense of effortlessness. The Williamson amp tried to be both. Triode connected KT-66s gave this amp the low-distortion loadline of triodes with some of the gain and efficiency of beam power tubes. This circuit and its siblings became the most popular tube amps of all time. It also created the most popular tube modification of all time: triode connecting multi-grid power output tubes.