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KOTriode wrote:

The Melquiades give me inspiration to build this 6C33C amplifier. It's on a stereo chassis that has few unique features - Vacuum tube rectifier separately for Input/Driver and Output tubes. - Regulator using the same tube types as the amplifier (for same sonic signature). - Direct coupling without capacitor in the signal chain (from input to output). I prefer this method over interstage transformer. - No negative Feedback. - Can easily be reduced to two stages.

Interning, KOTriode, thanks for sharing. Would you like to publicize the amp security?

The Vacuum tube rectification was greatly debated during the creation of Melquiades. My contusion was that if the soft-switching SS rectification is use and the most important if the input choke filters used with large last cap then there is no need in tube rectification. In addition, I was not able to get bass that I was after with tube rectification.

Regulator. This is a very interesting subject. There was a LOT of debate in Russia of regulator has to be used form 6C33C. Some people feel that it is very much must and others feel opposite.  I did single experiment regulating my 6C33C with 3x807 triodes. I was not impressed with the result but I do not insist that my result was definitive. The Jury about the need of regulation is still out in my view. Of cause the most powerful statement of the need of regulation for this tube would be the use of regulation in the best commercial amp built about this tube – Lamm ML-2.0. Still it was a commercial amp and it was “the Vladimir” – there are 2353 other sinister reasons why he would use more tubes in his design.  The reality is that I would be very interested to learn how he 6C33C behaves regulated and not regulated. The reason I did not go into the depth of this subject at the time when I worked on Melquiades was my modeling of regulation with my phonostage. I had built a very good regulator around 105V gas voltage reference tube, the 7788 pentode as Arial amplifier and 6C19P triode as the regulator switch. It was working fine (still have it), sounded fine but I detected that it a bit hold the Sound back and did not let to play with “hair down” if you know what I meant. At that time that slightly more polite and overly courteous  then I would like it to be sound of my Lamms ML2.0 power amps was exactly what I would like to defeat and it lead me to  abandon the regulation as the possible reasons for the “softness”. I do not insist that it was THE reason and I do not mind to try the regulation on 6C33C again. Sure, I will not be doing it now but I am still observing the commentary of others on the subject.

The direct coupling without capacitors or interstage transformers in the signal chain is fine. I juts a bit afraid of this 6C33C tube. It is not type 45 tube and not 2A3 that will run for 45 year with no sign of any problems. This is Russian 6C33C with own stupid behavior and ability crash. I do not know what kind driver you use but it get to be very reliable as if your driver in direct coupling application go down then your 6C33C will fry not only your speaker but half of your house. Talk to the people who use 6C33C for OTLs… BTW, when I saw you use 2 driver tubes per channel I though you use some kind SRPP to drive 6C33C…

Anyhow, it looks like nice amp. The design and assembling techniques are very pleasant. What driver and what kind output transformer you use? Did you find while you was working with 6C33C anything that I did not cover at my site? The most interning: how do you find your amp sound? Can you elaborate about the sound of the amp in greater details? Is anything that you learned, discover, realized from the sound of your amp?

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