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    Advantages of the ultralinear output stage

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    Bob Latino
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    Advantages of the ultralinear output stage

    Post by Bob Latino on Sun Dec 18, 2016 9:49 pm

    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




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    deepee99

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    Re: Advantages of the ultralinear output stage

    Post by deepee99 on Mon Dec 19, 2016 9:08 pm

    It was some poster here, or a link therefrom, who said running an ultralinear circuit in triode mode was like using just one pedal on a bicycle.
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    peterh

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    Re: Advantages of the ultralinear output stage

    Post by peterh on Tue Dec 20, 2016 2:12 am

    deepee99 wrote:It was some poster here, or a link therefrom, who said running an ultralinear circuit in triode mode was like using just one pedal on a bicycle.

    That statement seems ( for me) be applicable for a single-ended amp.
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    deepee99

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    Re: Advantages of the ultralinear output stage

    Post by deepee99 on Tue Dec 20, 2016 5:06 am

    peterh wrote:
    deepee99 wrote:It was some poster here, or a link therefrom, who said running an ultralinear circuit in triode mode was like using just one pedal on a bicycle.

    That statement seems ( for me) be applicable for a single-ended amp.

    Peter, you're right and I stand corrected. Although I think it could apply to triode v. ultralinear mode as well, metaphorically.
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    Peter W.

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    Re: Advantages of the ultralinear output stage

    Post by Peter W. on Tue Dec 20, 2016 8:40 am

    I dunno. It is an entirely funny thing how some proponents of the tube amplifier are striving to get "that first perfect watt" such that everything else, including a reasonable choice of other components is subordinated to that end.

    https://www.discogs.com/Saint-Sa%C3%ABns-Eugene-Ormandy-Philadelphia-Orchestra-Michael-Murray-Symphony-No-3-Organ/release/7664706

    This is my gold standard for testing systems from stylus to speakers. This was recorded a few blocks down the street from where I lived at the time and remains with me to this day.

    I do not believe that there is a single-ended audio amplifier on this planet than can do justice to this recording with any speakers known to man. I would further posit that a minimum of 100 watts into very efficient speakers will handle the greater-than-30dB dynamic range - much less reproduce the 30' bombard pipes - really more felt than heard.

    At the time, I used a Dynaco 416 into AR9 speakers in a room 15 x 27 x 9. Today, a Citation 16 into MGIIIas in a room that is 28 x 16 x 10. The 9s had a bit more bass. The Maggies are bit more defined across the midrange and treble.

    Thoughts?

    j4570

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    Re: Advantages of the ultralinear output stage

    Post by j4570 on Tue Dec 20, 2016 3:15 pm

    Peter,

    You brought back a memory using Telarc to test systems. I worked in car audio in the late 1980's and we did some pretty serious systems. Two discs we used were the Don Dorsey Bachbusters and Beethoven or Bust. Of course they were synthesized. Also, the Telarc sampler discs we had. My mother is an organist, and had the pleasure of playing a mechanical tracker pipe organ at our church (the bellows were intact and worked but an electrical blower was used).

    This at a time when RAP music was the norm used to test subwoofers. My boss would break out the Telarc discs and frequently most "boomy" systems clipped immediately due to the dynamic range. Organ Music is particularly challenging. And yes if you built the system correctly, you truly felt the bass. It wasn't all about power either, but good speaker design along with good amp design (enough capacitance for sustained notes). Another challenge with a car was you only had so much power, you couldn't plug into a wall.....

    Sorry to drift off topic, but Bob's post reinforces why the ST-70 (and now VTA-70) is such a loved amp.

    Jason

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