The British Valve Association (BVA) was a cartel of valve manufacturers in the United Kingdom of Great Britain and Northern Ireland (UK) that was designed to protect their interests from foreign competition. This cartel dictated (among other things), the price of valves (tubes) and how they were numbered (supposedly designed to make it difficult to identify American equivalents, which were typically half the price [retail] in the United States of America [USA]). However USA types manufactured in the UK by companies such as Brimar sold at the same price as their UK counterparts due to the BVA's insistence. All manufactures eventually published their own lists of 'equivalents' between their own valves and those of other manufacturers including American types, so cross-referencing became easy, in the UK at least. A cartel is a group of formally independent producers whose goal is to increase their collective profits by means of price fixing, limiting supply, or other restrictive practices. ... Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ...

The BVA dictated that no more than one electrode structure could be contained within one envelope. This latter point was because the BVA levied a charge of initially £1 per valveholder, to cover royalties on any of its members' patent rights. Pressure from set makers for multi-structure valves to overcome the BVA's edict lead to British and European manufacturers introducing many multi-structure valves and these eventually became the norm.

The British radio set makers were now able to adopt multi-structure valve designs. One German manufacturer produced a multi-structure valve that contained not only all the electrode structures for a complete radio receiver, but many of the passive components as well.