with these Russian tubes . Stay away from the 6n23p-ev and the 6h23n-eb. don't bother with any of the russian 6922 Electro Harmonix either .
The tube you want is the 6n23p or the 6h23n Voskhod 1975. It is the best sounding . the 1976 , 1974 ,73, 72 sound pretty good also . But clearly the 1975 single wire getter post (SWGP ) Rocket logo on the glass and the upside down flying saucer is the one to have . They are a pretty rugged tube also .You can find a nice pair on ebay for under 100.00 . Let me say again--- I know what I am talking about .
1975 Voskhod (SWGP ) Rocket logo on the glass (although I have seen some without rocket logo ) most have them.
one other thing---there is a Reflektor 6n23p and a 6h23n also . They are not rockets . Some people like those instead . I found that they sound good , but just a little thin sounding to me I prefer the Rockets
Hope that helps
Good luck--Steve