Cool! Man that Hera was a great deal, I would’ve bough it for sure. They’re hard to sell, but the sound quality you get for $2K is amazing. A hidden gem. IMO it showcases the 6H30 sound at its best - caveats aside (high gain, microphonics), in some ways I like it better than the much more expensive Audio Research Reference 6 (which also is a great manifestation of 6H30 sound). I just didn’t get that kind of "6H30" sound from the RP-9; must be the MOSFETs. I was certainly expecting it, and it wasn’t there - kind of a bummer.
Interesting about the report on Rogue’s Dark tubes - they couldn’t keep a large NOS stash around forever, so it’s to be expected. I think it’s more fun to roll your own, anways.
5751 can be a fun sub for the 12AX7 slots - they generally have a more precise, tigther image and better "clarity" and smoothness than 12AX7. 12AX7 tend have a bigger image and dynamic sound. At least that was what I found when rolling my original Apollos. Mazda Silver plate 12AX7 gave the best of both worlds, at the expense of a little extra treble energy (strangely enough, they have "T" plates like more 5751). Don’t get the silver-plate 5751 though - they’re brightness monsters.
As aforementioned, you can always sub 6189 and 5814 for 12AU7 slot. 5963 is usually too microphonic as a 12AU7 sub for preamp / phono amps, but it’s OK to use them here! The RCA 5963 are a nice tube for cheap. 12BH7 are more dynamic sounding and draw more heater current, but OK to use here too.
Enjoy! Hope your really like the Hera w/ 180 Draks. I know I would! I’m playing with Stereo 100 (non-Dark) and Hera in my 2nd rig right now. The ST100 is just a hero for its price point; such a fun amp and lots of tube rolling options - got Tung-Sol 7581A power tubes in there currently.