6N8S 6SN7 6Н8С tubes?

They are both soviet tubes, similar but some have larger glass envelopes.

NEVZ means Novosibirsk Electron Vacuum Plant

If ever in doubt you can always compare the filament voltage and amperage by googling the specs of each tube. It’s a good idea not to ever exceed the combined amperage to prevent damaging other components in your equipment.

I am no tube expert but is has been my past experience that tubes with larger glass envelopes generally seem to add to the 3D experience and sound more open and holographic!

I am no tube expert but is has been my past experience that tubes with larger glass envelopes generally seem to add to the 3D experience and sound more open and holographic!

 As far as price goes, I haven't noticed much difference.  Sometimes the cheaper ones have sounded better to me.  I guess it's a matter of individual taste. Doesn't hurt to try them though.  I currently only have 2 preamps and a pwr. amp that are tube and those are in a room that I hardly ever set foot into.  I've moved more toward solid state.  The only amps that I'll always continue using that are tube are my Marshall guitar amps.

Best of luck!