I’ve only got the original OE Chinese valves to judge them by but this’s what they say about the Novo…
"The Novosibirsk 6H6pi-N is a genuine Soviet design valve that has been used by many audio companies in the driver stages of their amplifier designs.
The Novosibirsk valve is a fantastic Audio valve and is the best sounding Russian double triode that we found for use in the Little Dot amplifiers. This valve has various identifying numbers such as -i. The Chinese name for the 6H6p tube is 6N6 as the Russian state that this is the same as ECC99 & E182CC
The Novosibirsk valve has a clear and well balance sound. This valve produced the best sound out of various types of valves tested in the Little Dot Headphone amplifier and offers an excellent upgrade to the standard Chinese 6N6".
After a little valve fiddle last night ooo er missus, I settled for the Novo’s and the 5654/EF95 RT which seems to compliment the 660’s perfectly, providing better instrument separation/sound stage, a fuller/richer bass all be not quite as quick as a solid state and the highs are warmer too but still manage to keep their pin point focus.
I’ll defo be rolling a bit more over the next few weeks and try the OE Chinese drivers again in comparison.