some info from amazon.com reviews:
SOVTEK EL84 SAME AS 6P14P STANDARD VERSION TUBE
By senorv6 on June 7, 2012
Sovtek EL84's actually sound well in a lot of amps compared to more popular tubes like JJ's or Electro-Harmonix EL84 tubes. In fact, some guitar amplifier manufactures build their amps to work their best with tubes like the Sovtek EL84. Sovtek EL84 tubes are also very durable and can handle more heat dissipation than other tubes in their class. And just in case anyone is interested, the Sovtek EL84 is the same tube as the Russian standard 6P14P which you can find in lots for very little $ online.
If you compare and examine the Sovtek EL84 and the 6P14P closely, they are identical in every way. And Sovtek's bigger brother, the Sovtek EL84M ("Military" version) is NOT a 6P14P-EV, even though many online claim it to be so. Upon examining the two tubes closely, there is a difference in construction. Also, the Sovtek EL84M is basically a 6P14P-K which was tested a bit more than a standard 6P14P tube against vibrations and can therefore handle more vibrations than a standard 6P14P tube. There is also other differences between a standard 6P14P tube, a 6P14P-K tube and a 6P14P-EV tube. For one thing, both the 6P14P and the 6P14P-K tubes sound basically the same tone wise and both have a life of 3,000 hrs (but at just 300 volts, they don't really last a full 3,000 hrs; more like 1,500 hrs or so). Of course, the same version of tubes produced in different years will sometimes have their slight differences in sound. Tone wise, the 6P14P-EV will yield more headroom in the clean channel of a guitar amp (it'll give you a "cleaner" sound) and has a life of 5,000 hrs handling up to 400 + volts. Sovtek EL84 tubes as well as Sovtek EL84M tubes are better suited for Cathode Biased amps where tubes seem to burn up quickly.
so its quite a good guitar preamp tube, right?