From SRPP and Mu-Follower to OTL Designs Tube amplifiers suffer from distortion. Fortunately, circuits such as the SRPP amplifier, mu-follower, and beta-follower produce minimal distortion even at output voltages of 50 to 100 Vpeak. These designs are often published with errors. Without a sound understanding of the theory, it is easy to arrive at a flawed design. In the first section of this book, we investigate the origin of distortion, while in the second we investigate the design of and SRPP and a mu-follower. On the internet we can find the most exotic designs. Evaluating them teaches us that these designs often make matters worse rather than better. In the chapter on incorrect SRPPs and mu-followers, we sometimes see bizarre and misguided designs where using a simple single-triode amplifier would perform much better. Push-pull output stages also exist. A great number of them are examined, and their similarity to the SRPP is discussed. This is done especially with the help of the theory behind the OTL based on the ‘mother’ of all OTLs, the Philips HF303. Finally, attention is given to frequency characteristics and technical matters such as the supply voltage and the filament power supply. To illustrate these points, there are a few designs covering the subjects discussed. This book presents much new theory that has not been published before. It is often an eye-opener, showing that many things have a beautiful and unexpected simplicity.
