get yourselves a voskhod 6N23p, you will thank me. i kept hearing people say it's basically a giant killer so i gave it a try a few months back. I like the zaerix 7 a lot myself, and have an array of mullards, teles, amperexes (bugle boys and orange globe) and although i am wanting to try a 60's white label us amperex - the voskhod 6n23p is what i keep returning to. i will never spen the insane amounts(for my budget) it takes to obtain certain tubes though. over 200 for a single tube aint gonna happen in this boy's rig. I find a significant improvement with the voskhod 6n23p over the Zaerix across the board. everything i'd read and been told about the voskhod was right on the money - there is nothing lacking in it. the highs are closer to the ultimately transparent and extended highs of the tele than my other tubes, there is PLENTY of body, the mids have only a touch of lushness about them (unlike the mullards) so they do the trick without being overtly euphonic, and the bass might be the best of all my tubes (deep, tight, detailed/transparent, a bit of punch). The best part of their sonic signature is that all of these elements are displayed in balance more perfectly than any of my other tubes, although i find that to be a strength of the Zaerix 7dj8 in my system.
i'm not sure what years to look for but apparently 70's 80's are the good old days. I received one late 70's and on early 80's and they sound alike and amazing. the 2 together cost maybe 40 bucks?
$200 for a single tube? For that much I would want a box of 20