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Melquiades Amplifier
Topic: 6C41C – the journey to nowhere.

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Posted by Romy the Cat on 08-24-2005

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It turned out that I made my Melquiadenisation with 6C33C. Not practically because it is good or bad tube. The choose of 6C33C was partially accidental: in the beginning I was trying to make an amp that would be able to work in multi-app configuration with older two pairs of Lamm ML2.... Since then when the ML2s were  left behind I kind of inherited the 6C33C in my Melquiades. Still I never had problems with 6C33C, neither with her capriccios character not with her sound. I have learned this tube quite well and gratefully keep using it.

Russians made a number sort of “similar” regulators tubes: the low gain triodes - 6C19P, 6C41C, 6C47C, 6C33C, 6C18C, 12C42?, different modifications, different manufacturing..... The 6C41C, 6C33C and the 12C42C are essentially the very same tubes but with different number of anodes... and consequentially with different dissipation power.

I use in my Super Melquiades (the schematic will be reveled as soon I will compile it into a useful document) a full 6C33 for LF channel, half of the 6C33 for mid-frequency and half of the 6C33 high-frequency channels. The half of the 6C33C does sound uncontestable better for higher frequencies and actuali it sounds so good that it does not sounds like a Russian-made tube anymore… Trust me, it is not my alleged Russophobia drives me to say it but the reality of most of the Russian-made tubes. So, I was thinking: if the ½ of 6C33C do performs so well in my application then why don’t I use the "normal" single triode - 6C41C.

The 6C41C (6S41S) is truly single triode - a natural half of the 6C33C and they are very much directly substitutable.

I spoke with a few guys who used 6C41C. Bas Horneman and some other guys form Germany gave a positive feedback about 6C41C. Anatiliy Monakov from Russia, who looks like he used 6C33C and 6C41C for quite long time and who sound very kindly and knowledgeably suggested me that 6?41C, in case power is not the factor, is a superior tube to the 6C33C and informed that the 6C41C is what he ended up using. I was encouraged and dug one tube while ordered few more. Initially the 6C41C sounded quite unpleasant as I used one tube in my HF channel. The HF with 6C41C and  a half of 6C33C in MF channels sounded dynamically and harmonically differently and it completely crewed up sound. My theory about an anal-retentive necessity to have identical amplifiers for multi-amping was proven again. Today I got more 6?41C and was able to use them in my MF and HF channels. The dynamically and harmonically differences were gone and the result .....surpassed all my pessimistic suspicions: the 6C41C is not as good as a half of 6C33C sonically.

Later on (few days), I will elaborate why I do not like what I heard. Now, my sentiments about this tube are too fresh and I would like to do more experiments to mature in my opinion.

Romy the Cat

Posted by Romy the Cat on 08-26-2005

OK, the amp is running for the 6C41C for a few days and it looks like the tube should be burned-in sufficiently enough for now. Still I have to note that the sound of 6C41C was not changed since my initial listening of this tube.

Originally I drove it with 235V and 100mA and then was dropping voltage to 150 and changed current. All together I figured out that when the tube dissipates 23W on it’s plate it performed it’s  best and Anatoliy Mankov suggested pretty much the same operation (190V and 125mA). Contrary to the ½ of 6C33 any further pressing forward the dissipation power in 6C41C did not change anything.

The fluctuation of gain among all my 6C41C tubes was even worst then 6C33C – I got 8 new tubes and they output whatever they wanted with a delta of 6dB. And of course… (and it typical among the 6C33C-like tube) the tubes had little to do with bias. To care 100mA my 6C41C demanded from –71V to –124V…. damn lovely!!! Well, I should not really bitch about it – that is kind of “fine” for the Russian tubes.
So, what was wrong with the 6C41C sound after all? The answer would be the 3 words: compression, compression, compression. The 6C41C is very much compresses sound, making dynamic range shallow and make sound like it hits a wall and then drop dead. With the half of 6C33C sound “pursues” to it’s abstract max dynamic value and then, after it reaches that pint, it ELEGANTLY AND GRACEFULLY comes down. With the 6C41C Sound reaches a dynamic max and then it got arrested by some kind of force that holds Sound in there. The ½ of 6C33C has some “signs” of sophistication at HF, in contrary the 6C41C makes HF less lucrative and more vague. The ½ of 6C33C is softer but at the same time is more “high-frequency self-sufficient” vs. the 6C41C that delivers juts “presents of HF” instead of a sense of “sufficiently compiled HF”…. In a way the 6C41C sounded like a worn 6C33C only 6C41C  is more compressed and slightly “fakeshly porcupineish”….

While I was playing with 6C41C tube I discovered another interesting behavior. The 6C33C reacts to voltage and current I fed it’s plate. I usually drive a half of 6C33C with 28W but if I give to plate more power then the tube response with slight but steady increase of output, sometime across the band and sometimes at the extreme frequencies (at critical power). After a certain threshold the response and decay at the top and bottom become screwed but still if I even load the tube with some kind of barbaric 450mA at 80W then it still change output with increase powers. With 6C41C it does not happen. As soon the 6C41C reach 230V at 100mA then any further increase of powers do not produce any reaction within the tube response. Here is a sweep of the Super Melquiades upper-bass channel (with high-pass filter installed between the stages). From those 23W I can go to 50W and analyze the response at 1/12 dB/octave but the 6C41C will not be reacting to raise voltage/current even at the frequencies extremes. In that the 6C41C is completely deferent behaves then 6C33C.

Anyhow, returning back to sound, I do not know how to explain the 6C41C’s sonic imperfections: by harmonic deficiencies or by necessity of the tube to care more grid voltage (less power) and as a result to drive itself “deeper” into class A1. I’m not a person who provide explanation, I’m juts a person who use those things. However I concluded that I will not be able to use the 6C41C and returned my Melquiades back to the 6C33Cs.

I do not know if my experience is indicative or not, your mileage might vary. If you do feel that you were able to get better result out of the 6C41C than let me know about my mistakes of blindness and I will give to the 6C41C a second chance. So far the idea to substitute a half of 6C33C with 6C41C does not sound potential.

Romy the Cat

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