<Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2006) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2006) (Learn how and when to remove this template message) </Td> </Tr> <P> 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). </P> <P>' 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 is sometimes confused with the more general principle of distributed loading . </P>

What is the difference between ultra linear and triode