The ultralinear circuit (which at the time was called a distributive load circuit) was invented by Alan Blumlein in England. He applied for and was given US patent 2,218,902 on June 5, 1937. Blumlein never really developed the circuit because he was killed in a wartime plane crash in July of 1942. In 1951 David Hafler and Herb Keroes created a “pentode type” amplifier in which the screen taps on pin #4 of the two output tubes were connected to the output transformer’s primary windings. Through experimentation they found that the best point to connect was at a point of about 40 – 42% along the primary winding of the output transformer. When Hafler and Keroes founded Dynaco in 1955, they used the ultralinear circuit in their first product, the Dynaco Mark II.
Ultralinear is a good way to get the low distortion advantages of triode mode and the power output of pentode mode. Ultralinear also gives the amp a lower output impedance than triode which translates into very good control of the speaker being used. Ultralinear also works well with odd loads and can drive electrostatic and planar magnetic speakers very well. All the VTA amps (VTA ST-70/ST-120/M-125) use an ultralinear output stage.
Shown below are three graphs showing harmonic distortion figures of push/pull output stages of triode, ultralinear and pentode connected pairs of EL34 output tubes. Also shown are the output stage schematics. Results will differ slightly depending on what driver stage is used to drive the output stage. The relative harmonic distortion figures, though, are always pretty much the same.
Triode > Harmonic distortions of the 2nd through the 5th harmonic are relatively low but power is limited … 15 to 18 watts is about all you will get with a triode connected pair of EL34’s. The 2nd harmonic is not too bad and the 3rd, 4th and 5th are pretty low
Ultralinear > The ultralinear amplifier has almost the same figures for distortion as the triode configuration but with a delivered power of 35W, about double the power of the triode configuration.
Pentode > A pentode configuration will not have the 3rd harmonic totally cancelled out. Although the 2nd 4th and 5th harmonics are low, the 3rd harmonic makes up most of the amp’s harmonic distortion and brings up the TOTAL harmonic distortion up to fairly high levels at or near maximum output.
Bob
Ultralinear is a good way to get the low distortion advantages of triode mode and the power output of pentode mode. Ultralinear also gives the amp a lower output impedance than triode which translates into very good control of the speaker being used. Ultralinear also works well with odd loads and can drive electrostatic and planar magnetic speakers very well. All the VTA amps (VTA ST-70/ST-120/M-125) use an ultralinear output stage.
Shown below are three graphs showing harmonic distortion figures of push/pull output stages of triode, ultralinear and pentode connected pairs of EL34 output tubes. Also shown are the output stage schematics. Results will differ slightly depending on what driver stage is used to drive the output stage. The relative harmonic distortion figures, though, are always pretty much the same.
Triode > Harmonic distortions of the 2nd through the 5th harmonic are relatively low but power is limited … 15 to 18 watts is about all you will get with a triode connected pair of EL34’s. The 2nd harmonic is not too bad and the 3rd, 4th and 5th are pretty low
Ultralinear > The ultralinear amplifier has almost the same figures for distortion as the triode configuration but with a delivered power of 35W, about double the power of the triode configuration.
Pentode > A pentode configuration will not have the 3rd harmonic totally cancelled out. Although the 2nd 4th and 5th harmonics are low, the 3rd harmonic makes up most of the amp’s harmonic distortion and brings up the TOTAL harmonic distortion up to fairly high levels at or near maximum output.
Bob
