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The 6C33C preamp? Hm, this is bold. As I see you use it as a single stage buffer with only one 6C33C and couple output with a transformer? I head the Germans built something like this but I never heard it or saw it. I do not feel a need for such a preamp, even though I drive very complex load.  Still, it is for sure interesting. When you fill conformable then writhe how it sound, particularly in context of a mandatory for any preamp bypass test. BTW, I can see in the back of the amp two tubes, looks like regulators. One of the tubes has getter all eaten up. I usually do not use the tubes with so dramatically eaten getter.

KOTriode wrote:

From what I remember from a tube dealer who said that these 6C33C need to have the heater burn for many hours before apply any current, if not the tube will have shorter life.

What your dealer advised is fine:  you can burn 6C33C heaters for many hours before apply any current.  I disagree that it will prolong the tube live but it will minimize the current swing during the tube break in. I do not recognize the current swing in the new 6C33C as a problem and I have given dental instructions how to deal with it:

http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=6140

Let look at in the process deeper. Reportedly when the 6C33C were made and the oxide-coated cathodes was activated some of the oxide contaminated grid that in a new tube begin to act as second emission devise in new tubes. As the tubes begin operation the oxides on the grid begin to burn out producing gases that are eaten by getter.  It is not know if the problem with 6C33C is due to the contamination of grid or die to the large amount oft left over gas in the balloon. In one way or another it looks like the heating up the tube for prolong time before running it at full power do help. It burns oxides from grid if they have any and it heat up getter, letting it to absorb gas from the tube.

What I do not feel comfortable, purely from practical perspective, is a recommendation to run the tube for a long time with heaters only. If you have a separate chassis to burn the 6C33C filaments then it would do but to do it on your main amp it is bit too irrational in my view. You need to put a separate swatch in the amp to hold the high voltage and you need to take the amp out of operation for long time – how you will listen music if your amp is busy with tube burning? With the same success you can get a party of your new 6C33C and dump them into kitchen oven at 320 degree for few hours. This will activate getter to do it’s duty and will help with some grid pre-burn.  To put the tube into the kitchen oven? Ok, not we are talking about the pure cooking with 6C33C. BTW, do not forget to put in the over some Italian herbs and paprika….

My methodology is much simpler in my view and do not take amp out of operation. Put the new tube at 20-30mA and in 30-45min you will have the max current swing the give tube will be able to demonstrate. You need to lower current constantly during the first 30-45min as it will/might go up and up. In my estimation what you start from sub 50mA you will not have during the first turn on more then 250-300mA. Eventually you will reach the point where currant does not grow. It will be it. This is the max swing. From now start to use the tube as useless. With the time, 12-70 hours of initial operation you will see that the current will be dropping and dropping, drop bias and give to tube more current.  The point is that if you use your amp let say 3 hours a day then it will let you to have your amp for 1-2 weeks perfectly operational while the 6C33C will be breaking in.

KOTriode wrote:

On my next mono block,  I will push them hard to get at least 25W with less than 5% distortion, that means run 2 tubes in parallel, but only one triode in each tube.

Why would you need it? I do not see any rational behind it.

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