I'm not convinced these are rare Stone. I just think there are few audio applications out there for online tube specialists to warrant stocking a lot, cryo'ing them, etc. Everytime I look on ebay they're out there NOS and not expensive. I got five pairs of three of the tube types for a total of forty dollars, and three of the five pairs were RCA, two were GE.

I also think that Steve ships the amps with a variety of different brands or at least others here have reported theirs came with different brands than mine did. Mine came with RCA OA3 tubes and Raytheon OC2 tubes.

I would recommend looking into OB3, OC3 and OD3 tubes. I've used the first two types and they do offer different sounds with the amp . . . I ended up pretty much preferring the OA3 type, but we're all differfent, our speakers are different, etc.

Stone, I have had good luck finding my various NOS voltage regulators, including both bottle and straight versions on fleabay.

Yep, lots of variables, and no way to get "absolute" comparisons or interpretations about something like sound considering various interpretations of semantics and tastes. And system and room is huge, but with the context of a system/room, adjectives appropriate to the particular values of what we are talking about, and comparisons, our common language can be useful at getting useful impressions across. This makes me think. It always seems to help me when folks list their system, and in the context of this forum, though still subjective, it could be cool to have a little room info or impressions in our forum system signatures. Hmmm.

Anyway, if we say "I like this" and that is all we have, it does not mean a whole lot. But with baseline context, attempts at good audio descriptors, and with comparisons of knowns, it may not be perfect, but it can be richer and easier to interpret toward personal ends.

For example, Lon has a lot of posts here that give a sense of his objectives, expectations, tastes and system. From this background calling the RCA OA3-ST "tart and dry" compared to the RCA OA3 straight means something, and to me was actually sort of revelatory. Especially since my idea of an RCA OA3 had until recently been only a 50s coke bottle shape, with no knowledge that the straight sided NOS RCA OA3 even existed. So when Lon talked about a RCA OA3, and since mine and his both came with the Torii, I assumed we were talking about roughly the same tube.

But back to the explanation thing. If we are familiar with Lon's preferences and system, his saying only "I like it better" is notably less information than the above, but still gives information do to extensive context. But without his system list and a background knowledge of what he likes, wants, and what he gets from his system, "I like it" means well, not much.

The thing in this thread I find particularly interesting is the direct comparison of these specific tube shapes NOS RCA to RCA, and it would tell even more if we knew vintage, and perhaps a few more descriptors, but to me, this comparison is quite useful and I would like to find some straight side RAC OA3s.

"SQ" I think we've been using on this thread to mean "sound quality."

I have a hard time figuring out what the Grid Mod does to the sound as I don't have a control for comparison. I have two Torris with the mod, and two other EL34 amps (Integrated and SE34 Monoblocks) without them. They sound different, but then two are Push Pull and two are Single Ended as well, so many variables.

Still seems to me that the mod is an amazing improvement that makes a big difference. But like will, I hear clear differences in the "signature" of power tubes in the Torii.  I've been very familiar with Winged Cs, and when I've had "Svetlana" tubes in it clearly has a different sound, and when I have had cryo'd Tungsol reissue tubes in they also sound differently. (I use the Tungsol reissues in my Torii Mk II predominantly; I prefer the Winged Cs in my Mk III.)

I have the impression that tube changes have an even bigger effect in the Integrated. When I change any tubes there, input, output, rectifier, there is a strong influence on the total sound output. I use cryo'd Mullard reissue output tubes there, I really like those; at some point I may try a quartet in the Mk III. Not sure if that is because there is no Grid Mod, or the fact that it's an even simpler circuit, or just my imagination. Anyway, I'm really enjoying the Integrated currently in my second system, where I don't need the power of the Torii amp. There's something about the SET "sound". . . not as precise as the Torii, but with just a touch of romance.

Hmmm. . . probably serves me better then without the Mod; I actually think it works very well with most recordings this way. Especially those my girlfriend loves to listen to, I've learned to like the music, but not the more mainstream pop production and recorded sound. Still, the Integrated manages to bring out a lot from Marc Anthony and Andres Bocelli cds.