The 6Ф12П is a not well known triode-pentode with quite unusual parameters - high transconductance and very high gain in both sections. Gain better than the 12AX7, but with fivefold transconductance - certainly sounds promising. Could be tricky due to microphonics and oscillations though. Works fine in line-level audio.
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2022-12-28 00:46:44
<span class="int-own-work" lang="en">Own work</span>