Special Quality (SQ) Tubes

The pinnacle of tube technology

Partly because of their pleasant appearance and high stroke factor, LF amplifier tubes (valves) in particular are very popular with audiophiles who speak about their favourite tube as if were is a bottle of ChateauNeuf-du-Pape bought at Sotheby's. Top of the heap are the rarer versions with gold-plated pins, the so-called SQ types, which are fanatically searched for, and often "fetch" more in cash than the heavy equipment from which they were pulled. Lesser known are the origins of these SQ tubes and for what purpose they were originally developed, which duly appears in this article, in summary.