Hi KT-88,
I had Almarro A318A & A318B integrated SET amps for about 4 months recently. Both use 6SL7 and 6SN7 input and driver tubes to drive the 6C33C-B output tube. The rated output is 18 wpc.
For comparison, I also have an Art Audio PX-25 SET amp(6 wpc), Welborne Labs DRD 300B SET monoblocks (7wpc), and an Audion Sterling ETSE EL-34 SET integrated.
My primary speakers are 95-97dB Cain & Cain I-Ben double-horns with the optional Fostex T-900A supertweeter. The FR is rated 40-36kHz. Along with those I have a pair of passive C&C Bailey subwoofers drivin by a IcePower 500ASP module amplifier. Check the rest of my system listed under my moniker. Secondary speakers were Jean Marie Reynaud Twins mkII monitors (90dB, 8ohm).
Anyway, on to the important stuff. I can't give a definitive description of the 6C33C-B's attributes because I have only heard it in this SET amp and never in any push-pull design.
But, my opinion is that the output tube via Almarro's design is extremely neutral and powerful with a crystal clear view on the musical material. Very balanced across the frequency range without highlighting any particular region.
Oddly, I found the A318B slightly hard sounding(not edgey) on the more efficient Cain & Cains. Not bad, simply more "up front" with a slight glare. The combination was never totally satisfying, although midbass and bass was great.
But, once hooked up to the 90dB Reynaud's, all objections disappeared. The A318B was really able to strut it's stuff. The tonality was rich and full with great dynamics and punch. This was match made in heaven. Midrange and midbass were spectacular. Bass was good (as far as I can tell with monitors). Highs shimmered and decayed without any hint of glare or edge.
As with all SET amps, midrange was where the magic happens. Vocals like Ella Fitzgerald, Nat King Cole, Sinatra, KD Lang, etc. had a full sense of body and tone. It was almost eery at times. Likewise, cellos and double bass had a great sense of wood and resonance. Even better was that the strings of those instruments were rendered with excellent detail and attack.
In comparison to my other amps, the 6C33C seems to lean more towards the neutral/accurate side of the fence than others. This isn't to say that the 300B, PX-25, and EL-34 are "colored" in comparison, just each has specific area where they clearly reveal "more" of a recording than the 6C33C-B:
The DRD 300B is a marvel of transparency and neutrality. It sheds all the typical lushness of other 300B amps(re: Cary) for a purer view. The amps have fantastic bass resolution and highs, but the real magic is their "spatial" rendering. There's a spooky sense of space created in a live recording venue or between peformers/instruments.
By comparison, the A318B w/ Reynauds provided an equal, if not greater, sense of depth at times. But, the soundstage wasn't as wide. The 6C33C obviously had more power and drive than the 300B's which tend to have a slightly softer more mellow approach to music. I prefer the 300B's on the C&C's and it is very close call on the Reynauds, partly because of the power difference.
The Audion EL-34 has a certain "tonal density" that is almost the exact opposit of the A318B. There seems to be more sound from within the recording, sometimes too much to the point of clutter. Part of this, I think, is due to a more diffuse focus than the A318B which tended to have better fine definition. I bounced back and forth between the two preferring one then the other. The A318B provided the more straight-forward, literal, presentation while the Audion leaned heavily towards the more lush.
Now, the PX-25, and this is an unfair comparsion because of it's 3-4x gigher price alone, features this amazing "lit from within quality" to instruments and tones. I've never heard anything like it before. Musical colors are much more vibrant and distinct. Across the board this amp outperforms all the others, as would be expected.
The A318B seems much more "dry" in comparison. Not bleached , just not as vibrant. Still rich, just not as much as the other amps. Although, it does impart a good sense of that SET magic.
I think is part of the reason why the A318B was not as great a combination with the I-Bens as these other amps. The Fostex drivers can be ruthlessly revealing in some situations and the A318B's slightly dry character ended up being accentuated, wereas with the Reynaud's (known for their warmth/richness) the A318B brought the performance a step back in the right direction. Adding greater focus and detail while retaining just the right amount of richness.
Hope this helps and sorry for the longwindedness.
