Around 2014 I started work on an amplifier. I started with the tubes and transformers from a dead Hammond AO-29. The preamplier and power section are based on an Orange OR-80 and Fender 5E3 respectively. Like the 5E3 it is a class AB push-pull amplifier with three preamplifier stages and a cathodyne phase inverter. I tried to make the amplifier as simple as possible, although did include the OR-80 baxandall tone stack for flexibility.

I primarily used Morgan Jones' books Valve Amplifiers and Building Valve Amplifiers. These books were written by a former BBC engineer and are thorough, readable, and filled with British charm.

The Aiken Amplifier website is also a great resource. Their article on "back-biasing" helped me solve a problem early in the process. Steve Henning of Henning Amplification was also a huge help.

You can hear the amplifier on Szasz Vol V in the music section. You can read about quantifying the technical aspects of the amp here.