The first Pure Class A amplifier Sugden produced was a power amplifier called the Si 402. The Si stood for Scientific Instrument and was part of a range of products produced by James Sugdens original company, Research Electronics.
Although thought of as a professional or scientific piece of equipment, it soon became obvious that domestic Hi Fi would be a far larger and more lucrative market. The Si402 was a 20 Watt design and sold in very small numbers under the new company J E Sugden. It later became the Richard Allan A41 and joined the Richard Allan A21 for a short time, before being brought back under the J E Sugden brand name.