Worst Sovtek product EVER!
Mis-matched sections, wildly mismatched, poor quality, just the absolute WORST quality EVER! Until New Sensor came out with the Tung Sol, this was the "only game in town", and New Sensor having no competition had no incentive to even try. Technically the 6EU7 shares the same gain, transconductance, and transfer curves as the 7025 12AX7 audio grade twin triode, but the REAL original NOS 6EU7 was supposedly a quieter audio grade tube, with a better pinout resulting in lower inter-element capacitance lower noise, and better H-K voltage potentials. Microphonics is usually not a problem, with the small plates, but try finding one with matched sections! These could draw as much as 2.8 or 3 mA of plate current, where a NOS Mullard might draw 1.4 mA, and 1.35mA. The adjacent plate on the Sovtek might only draw 1 mA, and triode 2 is drawing almost 3mA. That is just how absolutely terrible these things are. I scored a big box of English made Magnavox labeled Mullards, and tossed a whole case of the Sovtek 6EU7s in a junk bin outside. Maybe 1 in 12 is close enough to use as a phase inverter. As a reverb driver these are awful. As a first gain stage they are wildly inconsistent, and have about as much sonic character as a sack of dirt. Gain can be anywhere from lame to insane, but the high gain tubes tend to go bad pretty darn fast. Thank gawd New Sensor decided to make a better grade 6EU7, with their Tung Sol 6EU7 reissue.