GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Melquiades Amplifier
In the Thread: A different breed of 6C33C amplifier.

Post Subject: 6C33C amp/preamp follow upPosted by KOTriode on: 3/14/2012

Wow! I did not realized that almost 4 months have passed since I wrote last.
Quite a few things have happened the last 4 months that I have played with the 6C33Camp/preamp combo. I have tried at least 3 different vendors on the Ulyanovsk type, the Gold Grid plate (from Bulgaria) and Svetlana. The amp ran without any problem, I have modified the amp power supply by changing the power transformer to a beefier 400W toroidal, twice as much VA, so that I can experiment the 6C33C tubes with plenty more current and voltage. I changed the rectifier tubes from 5R4WGY to 5AR4. I ran the output tubes at around 220V and 240ma, that's about 53W of plate dissipation. The Bulgarian tubes after about 60 hrs of playing, showed instability in bias on both tubes, the current would changes every 15 minutes after I bias them to 220ma sometimes it will go up to 240ma, sometimes go down to 200ma, tube bias just dont want to stay put. After I got 20 new Svetlana tubes, I picked random 2 tubes, burn-in the heater for about 5 hrs, put on power, biased them at 230ma, it will stay the same times after times of power up and during long listening session. I have played more than 50 hrs on the Svetlana and quite happy with them. Few days ago I checked prices of these tubes, and was surprised that the asking price now is twice of what I have paid (and from same seller!) . The 6C33C Ulyanovsk in the preamp dissipate 6W of plate power ,worked without any problem, and very stable bias current. These 6C33C are suprising low in microphonic for an output tubes, I would say its microphonic level is as low as a good 9 pins or octal tube and much lower than any other output tubes.

I started to break-in the preamp/amp mostly with DAC sources but change to vinyl at about the 100 hrs mark and up to now, I believe I am familiar with the 6C33C tubes sound characteristic.

- Upon listening, one would recognize these 6C33C has huge and big sound, not too different from 845 tubes in what Romy characterized as Elephant Sound which not many other tubes that I have tried shares this same trait, and it is the main reason that I like the sound of 845.- The second character that stand out the most of the 6C33C tubes is the schockingly level of micro detail and focuses that these tubes revealed without adding a touch of brightness to the music when listening to a recording like John Klemmer Arabesque from Nautilus direct-to-disc. On a guitar recording of Kiyoshi Shomura playing Danza Espanola on the first cut, you can clearly hear the sound of the guitar string plucked and each breath the artist takes when playing. By comparison the 845 sounded dark and the leading edge transient is soften.- On dynamic, the 6C33C tube showed its ability to go deep in the bass on Ray Brown trio recording of Soular Energy which is excellent for a 15W SE , the 845 amp can do better, but not by much, but probably because of its 25W output give it more headroom than the 6C33C.- One always think that you have to use directly heated triode to get the best midrange out of a tube amplifier, the 6C33C proves that it is no longer necessarily true. The 6C33C is simply so revealing and coherent on pair of stacked Quad, it just sound much better than many amp in my stable, and that's include a pair of Futterman OTL 3.

- Distortion: the 6C33C is not very linear, in audio amplifier it exhibits the highest level of distortion than any power tube.

The 6C33C tube got to be the best buy tube in history, it provide so much level of musical enjoyment for such a price. In a multi-amp system, I would prefer to use the 6C33C for midrange and high, 100Hz up, I think it's hard to beat the 6C33C it's unfortunate that its power output is inadequate to power woofer even with one 100db/w sensitivity.

Rerurn to Romy the Cat's Site