It was back in the mid-'70s that David Berning made a name for himself in the Baltimore-Washington area as an avant-garde designer—someone with a truckload of fresh ideas about tubes. At the time, though Audio Research was starting to crank out pretty decent amplifiers, tube design was pretty much reduced to a rehash of the Williamson circuit and the Dynaco mod of the month.
A.C. Wente of Bell Telephone Labs was apparently the first person to get the bright idea (in the 1930s) of measuring sound transmission in a small room. A loudspeaker at one point reproducing pure tones of constant power, and a microphone at another point measuring sound-pressure levels, gave him the means to assess the room's impact on sound quality. The measured frequency response was so ragged that I'm positive the venturesome Dr. Wente was duly shocked.
Frankly, I'm fed up with the prophets of doom, those false seers who forecast vinyl's imminent demise. Some claim to have seen the writing on the wall as far back as ten years ago, sensing that the advent of the CD would perforce relegate the stylus-in-groove method of transduction to the trashpile of history. First of all, most of the music I enjoy happens to be on LP. And I'm sure I speak for many audiophiles who have also spent a lifetime building up a vinyl collection when I say we're not about to throw away our cherished treasuries of music. These LPs I expect to enjoy until the end of my time. Thus, I welcome any phono-system technological advance that will recover more information from the groove.
Lee de Forest filed for a US patent on his "Audion"—the first triode—on October 25, 1906, but never could explain why it worked (footnote 1). It was up to Armstrong and Langmuir, in their pioneering work, to place the hard-vacuum triode on firm scientific ground. When the US entered World War I in April 1917, the Army had to rely on French tubes. Six months later, Western Electric was mass-producing the VT-1 receiving tube and the VT-2 transmitting tube. However, it was only in the decade following World War I, as designers became conversant with the triode amplifier, that many of the crucial elements of tube amplification were nailed down. Technical issues such as coupling two gain stages and selection of optimal coupling impedance were already resolved by the mid-1920s. The triode ruled supreme until the tetrode came along in 1926, followed in 1929 by the pentode from Philips's research laboratories in Holland.