6C33-B vs everything else.

Ok this tube is making me wonder??? I know that BAT is running it in their tubes amps but I don't recall having the chance to hear BAT.

Can anyone tell me what the characteristics of this tube are? I am quite familliar with EL34, KT88, and 6550 output tubes so a compairison agianst one of those would be helpful.
The tube is only available from one manufacturer I believe. It is a warmer sounding tube than the 6550, but I found it to be less reliable and quite destructive when they failed in my VK60s. I won't consider another amp that uses this power tube.
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.
The 6C33C-B performed flawlessly in my A318B over the 4 months or so. Bias was rock steady without any hiccups. I had 3 Sets of tues and none gave me any problems.

The early prototype A318A was another story altogether, though.
Jeff. Per your thought that the 6c33c is quite destructive when they failed in your VK60s, and therefore you would not consider another amp that uses this power tube. Certainly any type of problem is a pain in the rear and I am sorry you had a bad problem.

It seems to me it is how the circuit in your amp dealt with the tube failure that caused the destruction you experienced. I am not aware that the 6c33c exhibits any unusual characteristics such that failures with that tube would result in problems that would not occur if a different output tube had a similar failure when used in the same circuit.
Wow! Spoken like a true audiophile. Except now you have me thinking about the 300B tube agian. I never did get around to listening to them. Do you think it would be worth my while to demo a integrated 300B amp? I would probally start out with something less expensive. If i liked it I could always upgrade at a later date.

Almarro is said to release details for a non-NFB version of the A318B. It's supposed to be warmer sounding with denser imaging w/o losing the dynamics. Maybe, you should contact your dealer about the retrofit
Hi KT_88,

You've never stated whether you are interested in a SET or PP amp and the type of speakers you have. Unfortunately, there is such a big difference in power output between the 300B & 6C33C-B (both SET & PP) that under 94dB and a fairly steady impedence your speakers will be a larger determining factor in the resulting sound than the amp. By that, I mean bass performance primarily.

300B's and 90dB speakers was good for most jazz trio, acoustic, chamber, and quartet types of music. Even most low key rock at moderate levels. But, if you still have the Quicksilver V4's and Meadowlarks, I think you'll find stepping down to 300B SET, or even PP, might be underwhelming. 120 wpc driving 89dB speakers gives pretty good control.


I actually sold the Almarro a month or so ago along with the Reynaud monitors so I could focus on just one system. To clarify my comments a little more, I don't think the A318B needs anything, it is excellent as it is. It just happened to be a little less than perfect with a very unique speaker - the I-Bens. That's just the way it is with single drivers, sometimes it works, sometimes it doesn't. 95% of other efficient enough speakers are going to sound awesome.

You have went to the trouble of researching me on Agon quite well. My complements to your industrious ambitions.

As far as what I have.....

I have done much traveling in the last 3 years and have sold all but my Meadowlarks. So basically I am starting over. Now the room I will be using for audio is not so large 16' X 15 'True the Kestrels are at 89db but, me being a person that works with things that are measured in db reference all day long, believe that I can get away with some things in regards to " what can or what will work "

I have long read about ( but have never heard ) the 300B tube. I thought perhaps if I could find the 300B in a PP setup running between 20-40 watts I could make it work in my system. I'm sure if I tried this by simply disconnecting something such as the V4's I would immediately feel I was robbed of certain aspects of my music. But I thought by finding a good integrated ( price wise ) I could hopefully enjoy the beauty of the 300B. I notice used 300B integrateds on Agon occasionally and thought I might try my luck with one. If i enjoyed the sound I could upgrade my speakers and even go to a SET 300B. I know it is possible after all my fuss I could very well go back to Quicksilver perhaps on a smaller scale of amp such as the Mid-Mono. But one never knows if is afriad to try.

Of course if there is someone out there that is crazy enough to let me demo their ( dealers included ) 300B amp. Feel free to write me :)
I actually have spent a bit of time listening to Meadowlark Kestrel HotRods being driven by a 300B Cary 300SEI integrated SET amp about 5 years ago. The sound was very warm, smooth, and engaging. A bit soft on the top and bottom ends, but I later realized that had more to do with the Cary than the HR's when I had a 300SEI at my house for a few weeks.

So, I don't doubt that you can get great performance from Meadowlarks and 300B's.

It's not clear whether you are hoping to find a 300B PP amp putting out 20-40 watts per channel or 20-40 watts total(10-20 per channel). 20-40wpc is nearly impossible with a standard 300B being kept within it's most linear range of operation. Most amp designers like to keep the 300B somewhere between 6-8wpc single-ended, 10 wpc is really pushing that tube to it's max cleanly. PP results are simply twice that amount. So, a really good PP amp that is staying in the sweet spot distortion-wise, will most likely yield 12-20 wpc at most. I know Cary and some other manufaturers like to claim 15-20 wpc single-ended, but that kind out output is highly suspect. It's possible, but you probably won't find them quoting distortion specs anywhere near their max.

Manley Laboratories makes the Neo-Classic SE/PP 300B amp that puts out 11wpp SET and 24 wpc PP. Their amps are extremely well made and sound fantastic. Not cheap, though.

The other options are amps running the monster 300B variants like KR Audio's 300BXLS tube. These puppys need a lot more current to run, but will legitimately put out 15-25 wpc SET. Although, if you simply drop these tubes into a standard 300B amp without current modification, you'll only get the normal 8 wpc.

Art Audio and KR Audio, itself, make 15-25 wpc SET's using the 300BXLS tube. They're awesome, but pretty expensive. I don't think I know of anyone making PP amps with them.

Don't write off 845 SET amps, they kick ass and I like them just as much as 300B's. You get 16-25 wpc of meaty, luscious, power with serious low frequency punch.

I think it will easier to find a great 845 SET than it will be to find a great 300B PP amp. Price-wise, neither will be cheap.
Hey Darkmoebius,

I'm reading your post and thinking hmmmmm.....

So you don't agree with the idea of a company such as Canary Audio designing a 300B amp such as the " CA-306 Stereo Power Amplifier " that claims to push out 24 watts per side with a total harmonic distortion of 0.5%?

And there are integrateds such as the CONSONANCE M100S-plus that claim to be producing 25 watts with less than 1% distortion. Granted this amp might not sound to best when it comes to 300B but I think it would give a person the general idea of what a 300B would sound like.

But if I'm not mistaken I believe Cary also produced a 300B stereo amplifier that boasted " 40 watts " per side! I had a chance to buy it on Agon for a song about 3 years ago and I'm still kicking myself for not doing it.

Or perhaps I simply misread your post.

And yes I was thinking of 2 channel PP output when I mentioned what I was looking for.

Just bouncing my ideas off of you as i have never listened to any 300B before. Unfortunately there are no dealers I am aware of that offer 300B, 845 offerings.
Hi KT-88,

I'm nowhere near an expert(or even novice) on power amp output, but 24 wpc 300B PP is really pushing the envelope for the standard type tubes. Although, great companies like Canary and Manly Labs(as I linked to) probably pull it off with flying colors. But, lesser or lower-end manufacturers claims in that range should be held suspect.

Go for one of those used Canarys, I bet they will kick ass with your Meadowlarks. But, don't leave the 845 too far off your radar, it's a monster.
Hey Darkmoebius

Thanks fo sharing your knowledge with me. But ah... don't be surprised if I change my mind completely and go with the 6C33-B amp I origianlly asked about. Or even if I go back to the Quicks again. I have am playing with the Quicksilver thought in my mind. I'm fickle that way. But then agian I could end up with 2 or 3 amps before it's over.

thanks agian!
Kt 88, I have an alternative suggestion for you to consider: Quicksilver Triode monoblock amps. These fine unadvertised hand made beauties utilize one pair of 6C33's in PP fashion generating a credible 50 watts. Mike Sanders designed and builds these to be his statement product, and succeeds quite nicely IMHO. Darkmoebius described the sonic character of this tube exactly, just like Goldilocks and the three bears, not to sweet, not too lean...just right! With base going down to near DC, and upper frequencies that extend to the clouds there is nothing I don't like about these tubes and these new amps. Consider this long-time EL34 enthusiast a convert to the 6C33!
FWIW, the 6C33C-B is out of production and is not expected to go back into production as the plant that built it is gone- closed about 3 years ago. There is a substantial stock of the tube ('thousands' according to one distributor) still available.

Compared to most power triode tubes the 6C33 has a relatively short service life. The Russian data sheet specifies 750 hours, although in practice you can get up to 2000 hours if all goes well. On account of its filament circuit, the tube runs *very* hot!

Another thing you will want to consider is the socket issue. The socket is a septar type that was originally used by the American tube type 3C33. The Russian 6C33 has considerably higher filament current and the socket was not designed for that sort of service and so has a very short service life.

Anyone who runs a 6C33C-B amp using the Russian socket knows what I am talking about. The contacts begin to fail due to corrosion and weakening of the contact springs. They can be re-tightened, but ultimately the socket has a service life that is in the region of 5000-7000 hours. The American made version of the socket does last longer but is much harder to obtain and is not cheap.

FWIW we made the first American-made products using this tube back in the early 90s. The short service life of the tube and its socket made the tube unattractive.
Hey Badboss429,

I like the look for the Quicksilver Triode. But would like to find one used as my budget wouldn't work for new. I have also found a few other amps that use this tube I'm looking at. I'm in no hurry I geuss. But ultimately I will buy something.

Atmasphere ( with a name like that you must be a OTL guy ) Nice to know about the socket for the 6C33-B. I would be curious if BAT and Quicksilver employ the American version. I'm guessing the cheaper priced amps defintely are not.
I've owned amps from Quicksilver and their quality (both performance and reliability) is fantastic and they are one of the best providers of service in the industry. If you can find one in your price range, I'd explore Badboss429's suggestion.

I owned a Joules Electra amp that utilized the 6c33c tubes. These amps were designed by a true artist who knows his stuff. The tube life within this circuit was quite lengthy. The sockets were without any problem, either in corrosion or contact spring issues. In part, I assume the reliability of these amps and the longevity & freedom from the issues described by Atmasphere is due to the reasonable bias currents utilized within the Joules design.

I had a bud who owned the Atmasphere 6c33c amps and their bias requirements were double what Joule uses. He had a need to replace the sockets about yearly and had constant tube issues.
KT 88, Call Mike Sanders at Quicksilver Audio and ask about tube and socket life. When I inquired, Mike told me that he runs the 6C33 at low stress levels and expects extremely long life out of both (in contrast to other manufacturers that push these tubes hard ex: Tenor and Lamm). Retail is $5800 for the pair, but a nice dealer demo pair could be had for $4200? World class performance for comparatively little money IMO.

My mouth is watering, but I'm not reaching for my wallet yet :)
I can vouch for my good friend Dennis' (Badboss429 - wish you didn't sell that Boss 429!) enthusiasm over the Quicksilver 6C33B monos.

We got together last Saturday so that he could get my impressions of them, I have to say they won me over. Enough power to do the job, terrific bass weight / extension / fullness, a great treble, and for him, the most important characteristic, a sweet, musical midband. To my ears, they offered the unique combination of what we seek in the EL34 tubes - midrange, with what the larger tubes provide - bass, with seemingly no tradeoffs. The blend of just enough richness, body, and liquidity with clarity and openness is a rare find. Not really sure of another amplifier at $5800 that bests them. You may have preference for a different flavor, but that would be just that, different, not better.

We're getting together soon to listen to them side by side with my Jadis and AtmaSphere amps - definitely a murderer's row of amplification. I'm sure it'll be another fun day.

By the way, AtmaSphere is not an OTL guy, he is THE OTL guy - Ralph Karsten, owner of AtmaSphere.
Thanks for the kind words Joe, I can always count on you to accurately describe the things you here(far better than me and most I may add).
Please note that I am not a Quicksilver dealer, just an enthusiastic owner of Mike's products for 21 years.

I guess you never know who your chatting with here. I think that is the neat thing about Agon. We are all on the same page ( literally )

I myself am just a guy the loves audio at the lest possible price, with the maximun possible quality. I got annoyed with the computers that are sold on the store shelf. None had what I wanted and din't want. So I finally got the courage to build my own. Most likely some day I will do the same with most of my audio gear. But for now I am inclined ot buy my gear.

Those Quikie Triodes are still making my mouth water though!