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"At 4 ohms, output drops off to around 19Wpc, which is a bit ridiculous for a $288 amplifier."

I've used OTL amplifiers exclusively, for the past nearly 50 years. From the mid-70s and up to around the mid-1990s, I owned several different pairs of Futterman amplifiers and used them to drive either one or two pairs of KLH 9s, depending upon my living space at any point in time. With two pairs of 9s run in parallel, the bass was thunderous. With one pair, not so much. But it was common knowledge that a single pair of 9s would not make much bass, in part because of phase cancellation and in part because of the limited radiating area. Nevertheless, I am kind of puzzled as to why JGH got poor results in low bass performance with the Futtermans driving 9s, compared to the Marantz 9s, especially since most ESLs tend to exhibit impedance maxima in the very low bass that I would have thought would stress the Marantz. I have made impedance vs frequency curves with my full range Sound Lab ESLs, and the impedance below 100 Hz goes sky high, 50 to 100 ohms at 20Hz. I assume the impedance of a KLH9 below 100Hz would be much higher than its stated nominal impedance of 16 ohms. The Futtermans should have been able to drive the 9s at low frequencies at least as well and maybe better than any of the two transformer-coupled tube amplifiers that were compared. I can only think that the review is from 1970. By the time I got hold of Futterman amplifiers, Julius had dramatically increased the coupling capacitance to at least 1600uF, IIRC. Maybe that was the problem. Maybe also the low frequency load presented by the KLH 9s to a Marantz 9 or Dyna Stereo 70 was sufficient to generate euphonic harmonic distortions in those amplifiers. (Grasping at straws here.)

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