The Wattkins Universal PCB is one of the basic building blocks for building a guitar amplifier with up to four vacuum tubes. It supports most amp designs (it started out life as a Fender 5E3 Tweed Deluxe), including support for Paraphase, Cathodyne and Long Tail Pair phase inverter as well as Cathode or Fixed Bias. As well as the more common 12AX7 & EF86 pre-amp tubes, it also supports Russian pre-amp tubes such as 6N2P & 6J32P with the heaters on pins 4 & 5. Output tubes supported include 6V6, 6L6 and 5881.
The View From Simon Higgs' Cranium