I guess you guys were not around when Audio Research rose to pre-eminence based mostly on HP's adoration of their amplifiers and preamps. The SP3 preamp went to 3A, 3B, etc, in a matter of several months. I cannot even remember where it all ended with that model. The Dual 50 amplifier rapidly went up to at least Dual 50F-1B. On the amplifiers, it was almost a necessity, as the Dual 50 had a habit of blowing up for one reason or another, and Bill Johnson was constantly making changes to improve reliability, which in turn affected sonics. My good friend, who owned a Dual 50, was in the habit of saying that the amp was only safe when unplugged.VPI changes names, rather than adding suffixes.
