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Laurent,

The V2 in 6C33C does NOT need to be matched by other characteristic then gain and it is very easy to do. If you have two V2 tubes and they have different entry points for bias but the same gains then you will not detect any sonic consequences – it was tested many times by me.

About your first problem would be more complicated to tell from distance. The ML2 has a regular voltage regulator based upon a voltage reference tube, pentode amplifier and the 6C33C that serves as regulator (V1). There are many different versions of voltage regulators that sometimes they are called Error Amplifiers. I do not know what Lamm implemented in there but ALL regulators are VERY simple and it hardly anything might be broken in them. Make sure that the gas tube went off and that is has the reference voltage on it. Make sure that the reference voltage from the gas tube is delivered to the amplifier cathode. Make sure that the voltage from amplifier plate goes to the regulator grid. Replace all 3 tubes and checked above. If Lamm used a shunt regulators (that is possible if you have LOVER voltage) then anode of all 3 tube are combined with juts a control amp having a plate resistor and it would be even more easy to debug. I still feel that nothing shell be wrong with your amp as there is nothing in there to fail. Check the contact on the tube sockets…

BTW, if I had ML2 I would try to use it with no regulation of V2 plate at all by disconnecting the regulator. I am NOT saying that it would be better – I do not know. And what I have my ML2 I did not try. I was trying to run 6C33C from my .5A Fluke tube regulator with 3 paralleled 807 triodes as regulators and I did not like how the 6C33C sounded. The 3 paralleled 807 gave the same or even lover output impedance as one 6C33C still with 6C33C it might be different. It is not to mention that different regulators do sound differently. I just afraid that with no regulation ML2 would need to have different PS as it’s ripple and current stabilization characteristics would not be optimum. Anyhow, I do not reinvent the ML2, it is what it is and probably to try it without regulator is not a good idea.

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