The Williamson amplifier is considered one of the earliest hi-fidelity audio amplifier designs. It is certainly one of the most popular audio circuits ever developed for DIY’rs. Without fail I seem to turn up at least one home-brewed Williamson every year at the local estates+fleas. A PS Dot Com reader from the UK sent us the original articles from “Wireless World” as published in 1947. I have yet to build a pair of these myself, and the idea of starting ‘from the top,’ as it were, with the original design, is appealing. A few things to note: check out the provision to balance the driver stage, and separate bias level and balance controls for the output stage. Also: check out R25: the formula for determining the feedback loop resistor. I wish every schematic included this notation. NB: the ‘L63’ valve is simply a 6J5 – aka, one half of a 6SN7. the ‘U52’ rectifier is a 5U4 or equivalent. ‘KT66’ is a better-performing 6L6; feel free to use 6L6 or 5881 if necessary.