set of 4 vintage black plate audio preamp tubes, legendary tone roller quad

12at7wa pair w/ made in usa etch and halo getter matched internals, faded labels

12at7 pair w/ straight/angle dgetters and similar plates (1 rca logo visible, 1 raytheon?)

carefully curated from old collections

full amplificaton test 110/108~130/130 (d) 120/120~122/125 (halo) % mutual gm (65 % good)

simply put lower gm = more head room and tamer bass, higher gm = x gain / bass response

our unique mutual gm output test applies 225 vdc simulating actual circuits plus filtered dc

push pull setups and high end designs require < 10% triode match, lopsided gm = better for mono apps

also supplier tested via tv7 for conductance + life leak short gas checked

all open box tubes undergo a complimentary proprietary one of a kind master refurb process!

give 100+ hours at your specific amps voltage to fully cure due to long term hibernation

ships fast well packed worldwide, combined post available

~authentic vintage hifidelity audio curation by caliacoustics~