After having Sonic Frontiers SFC-1 more than two years, I have come to conclude that it is one of the most underestimated amps in the high end used equipment market. It is truly musical and assertive amp without colorations of classical tube amp.It can use different output tubes from EL34s, 6550s to KT90s. Its construction and parts quality are first rate assuring long term trouble free ownership, aside from the usual need to periodically replace tubes. The output tubes can be biased easily via flat-head screwdriver from the back externally accessible adjustment controls. This is an amp for serious music lovers with financial restrains
