Ultra-linear

Ultra-linear electronic circuits are those used to couple a tetrode or pentode vacuum tube (also called "electron valve") to a load (e.g. to a loudspeaker).

'Ultra-linear' is a special case of 'distributed-loading'; a circuit technique patented by Alan Blumlein in 1937 (Patent No. 496,883), although the name 'distributed-loading' is probably due to Mullard. In 1938 he applied for the US patent 2218902. The particular advantages of ultra-linear operation, and the name itself, were published by David Hafler and Herbert Keroes in the early 1950s through articles in the magazine "Audio Engineering" from the USA. The special case of 'ultra-linear' operation falls under the more general principle of 'distributed-loading'.

Operation

A pentode or tetrode vacuum tube (electron valve) configured as a common-cathode amplifier (where the output signal appears on the plate) may be operated as: