tube purchased paired quad (4 tubes) fitted to my Hiwatt Custom 100 clone played with a bass.
Russian-made tube is wanting to be a true copy of the Sylvania 6CA7.
concretely it is a tetrode (like a 6L6, 6550 ...) with the electrical characteristics of an EL34 (compatible so).
building level tube is rather solid and well full, the cathode is very similar to a cathode of 6550 in a modern 6L6 tube.
the cathode and more equipped with small fin to improve heat dissipation.
robustness level, I think it is a rather very strong tube that has undergone many malmenage in my amp (test phase biasage very hot ...) without flinching or blush. reliability looks good.
its level: closer to a 6L6 or EL34 6550 as a, loose sounds very low, low compression, medium a little behind and acute putot lens (not too intrusive). In short it makes a fairly low (well rounded tone). lots of headroom, you can push a lot without it saturates.
Conclusion: Sturdy tube, reliable (compared to a quad of JJ KT77 just slamming me in pognes after 10j ...) and not too expensive (€ 60 for a count paired quad). very good value for money, I think I apportion the above without taking risks.