The "textbook Heerlen sound" has been referenced in several Soundlumia listings of Amperex Holland 12AT7/ECC81 tubes, and many tube enthusiasts asked what that all means. So this is the answer: the late 1950s and very early 1960s tone, the beginning of over a decade's excellence in sound, the classic tonal template for all the great (and greater) Amperex/Philips/Valvo/Miniwatt tubes to be made in the years to come, the timeless Philips radio tone that many of us grew up listening to.
The most distinctive sound feature of the Heerlen ECC81's is the transparent, natural and expansive midrange presentation, with a slight touch of warmth that illuminates your music. Every piece of music you play through these tubes sounds like from a vinyl record, whether your sound source is phono or not. The sound stage is spacious, deep and structured. Bass is incredibly deep but well controlled and feels as accurate as on the high end German ECC83's (Siemens, Telefunken, Valvo etc.) Thanks to the very rare foil d-getter on this pair, you get with fast response (as in the solid-state fast), overwhelming detail in sound and the realistic bass.
