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Morricab,

I do not know the “truth” and what I said are pure my speculations based upon what I hear and what I measure.

Yes, Lamm drivers at 310mA quite hard but do not forget that his objectives, besides everything, were to get out of his SET max power in order to enable his customers to drive speakers with sensitively of 90x. Defiantly the lover plate current will prolog the tube life (and with appropriate transformer, in case of SET, will make bass better beside other things)

Regarding what you said.

First of all I think we should stop to refer to 6C33C as to some kind of crazy military tube used in aircraft radar power supplies. This is the stories that the marketing people drop to the head of literature-loving gullible audio people and they spread the myth. The 6C33C was designed as the powerful voltage regulator, the same as 6C19P, 6C18C, 6C41C and the rest. People in 1961 regulated voltages not only in the aircrafts. I remember Lars Fredel was blabbering that 6C33C was specifically made to use in Mig-29 radar power supply. The Mig-29 hit the design boards 20 year AFTER the 6C33C was mass produced. Also, how many those damn tubes is necessity to supply the aircraft demands? Victor Khomenko (from BAT) told that during the pick of the 6C33C production Russian made 100.000 tubes per month.  They did millions of them as still do them. Who the hell need them today in the aircrafts? Interesting that some of my Russian sources informed me that the 6C33C that were actually used in the aircraft radar power supplies were very much deferent (for instance golden plate and so on…) then the 6C33C that we stick into our amplifiers.

Second, let do not forget that the 6C33C used as a regulator dose not need a lot to regulate. The regulator tube in Lamm ML2 might be old and completely dead it still regulated perfectly fine and the amp sounded OK, even the regulated tube was completely unusable in the V2 position (the sound tube). In some other cases that regulator tube still fine measurement-wise but sonically it is dead (example is the 6C19P in Lamm’s L2 preamp, where the regulator sonically dies in 2-3 weeks) the point that I ma trying to make that the requirement that we have in audio are different than those that the engineers apply to the voltage regulators. I think we should consider that regulator tube is dead what it sounds bad not when it stopped regulate or when the tubes’ cathode emission reached a certain point. In most of the cases it does comply with some measurable of observable data, in some rare not really. Probably the different things should be analyzed with the different tubes, I do not know. In case of the 6C33C it is even more completed as they are very different to begin with and made according very not stable specification.  Some of them handle abuse very very nicely and some of the chock with 200 mA….

Generally if you do not stress them (play loud) when they still cold (15-20 min) then they behave much better in the long run….

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