12ax7 ecc83 cv4004 5751 e83cc ecc803 6057 6681 7025 7058. the high power 5751 are premium 12ax7 ecc83 w/ slightly less gain, introduced in 1949, as military spec and industrial grade. originally designed for aviation, the costly triple mica design is rugged + less prone to microphonics, w/ higher power at 175ma.
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