The Fender® Bassman 5F6-A, 3rd Edition
by Richard Kuehnel
The Bassman was introduced in 1952 as a bass guitar amplifier. It had a huge 15-inch speaker with a closed back and used a pair of beam power tubes for lots of volume. Throughout the decade it would be modified and improved until culminating in the model 5F6-A. A legend was born.
Ironically it didn't quite make it as a bass amp, but the musical tones it created from a guitar made history. The Bassman's long-tailed-pair phase splitter with negative feedback became the foundation for many great rock and blues sounds. Many other amplifier manufacturers created new Bassman-derived designs that themselves became the legendary instruments of a rock generation. For more than four decades the 5F6-A circuit has been tweaked, enhanced, and re-introduced under many different logos and the late-1950s original has become one of the most collected guitar amplifiers of all time.
This book examines this famous amplifier by studying its circuit design in great detail. It starts by breaking the amplifier into its major components: the 12AY7 preamp, the 12AX7 voltage amp, the 12AX7 cathode follower, the tone stack, the long-tailed-pair phase splitter, the push-pull power amplifier, and the power supply. Each component is analyzed to determine how it works and to derive the design formulas needed to predict its performance. The results are then compared to bench tests of the actual circuit. Finally all of the components are put together to analyze total system behavior and to discover how and where the amp transitions into distortion.