Never seen "OC" before but have seen some pretty cryptic lettering using the same black typeface added to these tubes.

If they were really for aerospace, they might be a special culling of very low microphonic tubes which should make them sound better and without using tube dampers, but who knows.  Might also be extra strong, high output, another desireable characteristic.

If you get some (they're cheap enough to be sure), please report back on your findings.  Also, all of these tubes tend to sound better and last longer with cryo treatment.

Put another way though, I'd bet they sound at least as good as the EV issue.  Hopefully, even better.

Zencduser,
Did you ever order these? What do you think?
Thanks,
John

I have recently ordered the 6N1P-EV "OC" version from a Ukrainian store which was closing down due to war.  The seller said the "OC" version was prohibited from export as it contains gold.  This tube sounds more than excellent as compared to the overpriced Telefunken E188CC.  While the Telefunken is "low noise", the "OC" is ZERO noise.  Secondly, this "OC" version generates great sound stage.  It is currently very very hard to find this "OC" version in the market.

Quote:


I have never bought tubes from Tube Museum, but they seem to have an excellent reputation. However I find their listing confusing at best, and completely wrong at worst. I have never ever seen a Soviet made tube with an EV-OC suffix. I have seen plenty of tubes with the -I suffix for pulsed operation. And my understanding is exactly the opposite of the quote from the ebay listing:

"THE I" version is for pulse operation - and also it is 500 hours variation of the tube.... the one without the "I" is the one that can be used 2000 hours....  it seems that "I" one is no good for me

The way I understand it, the -I suffix is optimized for computer use, where it is used for pulse i.e. switching operation and spends a lot of time in "cut-off." Cut-off is where the tube is on, but not conducting between the cathode and the plate. This is very hard on the cathode, so tubes that are optimized for pulse mode have double extra thick cathode coating and in fact generally have much longer life when used in audio circuits compared to "regular" tubes.

How they sound is a different story. The only -I tubes I have used were 6N3P-I, which are equivalent to the 5670/2C51 tube. And they sounded horrible. But so did most of versions 6N3P tubes, so I wouldn't make any sweeping generalizations based on my limited experience. But I would not hesitate to buy -I tubes, they do NOT have a shorter lifespan than others.

JMO/FWIW/YMMV and all that.