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Is this still a problem with ultra linear tube amplifiers?

Posted by Vic D on July 7, 2012 at 20:49:29

In the process of selecting a higher powered tube amplifier I came across this Bob Carver interview regarding ultra-linear. I'm assuming that with their popularity and continued production that the issues mentioned in this article have been worked around by now.

["I met Stu Hegeman when he went to CES to show his new Happi One preamp. He told me that ultra linear was the worst fad of all time, that he only designed one that way, that it was the biggest blunder of his career, and he would never design an ultra linear output stage ever again. And he didn't. He designed lots of amps for Sidney Harman and for Lafayette, and only one was designed to be ultra-linear, the Citation II. Sidney, his boss, made him run the KT88s at 0.100 amps per tube with 500 (earlier) volts on the plate at idle (see Sam's photofact). 50 watts for a tube rated at 35 watts! Sidney wanted to have low distortion to compete with Marantz. Stu objected, but Sidney made him. He relented after too many tubes blew up, frying the screen resistors and the Citation division of Harman Kardon had to fix them all."

"The other problem with ultra-linear is that the screen grid is pushed too low when the plate pulls close to ground at high output. This limits the maximum output current to a rather wimpy value and makes the amplifier's power response very peaky, falling off rapidly as we go away from the ideal loading. Speakers do that. Stu taught me all this one enchanting day at CES. Before that I believed everything I read about ultralinear as being the cat's meow and the hot set-up. Then I noticed that the tube amps I loved the most were pure pentode, not ultra-linear (Citation V, Lafayette 550, Mesa Baron, I could go on and on). My heroes are Einstein, Gandhi, Hegeman. Hegeman got it right. So much for Ultra Linear!"]

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