I've been playing around with my rig and I have another $0.02 to add.
I think speakers / cabinetry is of utmost importance in getting a good low volume tone. My Mock212B* build project from the summer is curious because I built it for loud volume situations. What I discovered is that for whatever reason, the dimensions of the cab + the speaker combination (v30 + c90) just work pretty much perfectly with a recto. I was running Yellow Jackets today and I noticed with a bit of EQing a good tone can be had. It can get quiet enough that you can hear the guitar pick loud and clear but it isn't exactly 'quiet'. As you turn down the amp further, it just doesn't put out enough oomph to really move the speakers. To get rid of the over bright high end of the EL-84s, I ran my 2 channel recto on red to vintage and lowered the presence control on the red channel. Then I turned the orange channel presence up to add cut and sparkle to the extreme highs. I then dialed back the mids somewhat to make a 'bigger sound'. With the EL-84s you don't quite get the gut busting horsepower as you do with a 100watt head.
With this speaker combination, I'm beginning to think that the fizzies people complain about are at least 50% a low volume speaker artifact in the sound. i.e. related to v30s. My thiele 2 x 12 is supposed to be for low volumes but strangely enough, it can get really fizzy at low volumes while the Mock212B does not. It seems like it emphasizes the treble and presence frequencies more while the larger Mock212B has much more brilliance in the high harmonics at loud volumes. The only real 'fix' for getting more speaker movement at low volumes is to get a low wattage and less efficient speaker. Say a Greenback, for instance. A G12m Heritage and a G12H Heritage (WGS Green Beret and Reaper 55Hz) would most likely be a great pair for this. The lower wattage speakers sound 'looser' and 'more open' at low volumes which allows for the sound of the amp being more cranked. (the downsize is that you need a cab with more robust speakers for LOUD volumes and in my experience, it really makes little difference) In a perfect world, I'd build another Mock212B and load it with these speakers, just to see if it would work. Still, it sounds awesome so I don't want to ruin a good thing.
At this point, I think it is safe to say we are quibbling over minutae. Even with running two EL-34s on spongy, I can get my amp down to 'I can hear my guitar pick' levels. I can record my gear and prove that you can hear the pick. If this is still 'too loud', then people who complain seriously have problems. I think in my quest for great tone at low volumes, I have basically reached the absolute physical limit of the technology. Furthermore, in my experience, there is absolutely NO difference in volume between 2 EL-34s on spongy with a tube rectifier and 2 EL-84s / Yellowjackets. The real difference is actually in TONE. The EL-84s change the tone of a Dual Rectifier in a big way. The clean is hands down a MASSIVE improvement. The amp thinks it is a Vox or an 18 watt plexi. Something like that. The gain tone simply changes becoming much more vintage and mid focused. Initially it will sound very thin and bright, ESPECIALLY on the modern channel. As discussed above, manipulating EQ settings on the amp can smooth things out and yield usable and even good tones.
I guess if I was to distill this discussion, I'd go on record to say that there are two things that make low volume tones far better with a Recto.
1) Yank one rectifier tube and two power tubes. (run on spongy if necessary. Also use EL-34s)
2) Get a great sounding cab / speaker combination. I find a 2 x 12 is ideal since it retains beef but the speakers move more because there are less of them than in a 4 x 12. (I haven't heard many 1 x 12s that can do a great crunch. They usually sound thin) The oversized 2 x 12 with a ported centre baffle really mimics the sort of frequency response the Dual tone stack was originally designed to work with. Furthermore, the c90 really mutes the fizzy frequencies while v30 in turn adds definition to the tone. You end up with a much better lead tone, a rich and detailed clean, as well as a phat and meaty rhythm tone. It is very traditional mesa cab tone though. It isn't like a g12m 25 or other vintage speakers which give so much more brown and woody of a tone.
*Copy of a Mills Mach212B
But as most people have said the rectos are mostly preamp gain so attenuators wont really do all that much at bedroom levels. I use mine with the channel masters about 10 o clock and the output volume at about 7 o clock and its a grand volume for bedrooms i think
