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In the Forum: Melquiades Amplifier
In the Thread: To drive the 6C33C...
Post Subject: Re: Cracking the 6C33C.Posted by hagtech on: 3/22/2006
I think you'll have trouble adding a copper sleeve to the power tube. The thermal coefficient of expansion for copper is probably much greater than that of the glass used. Hence, the copper will enlarge much faster and break the glass. It's a good idea, just the wrong material. Obviously you are familiar with the water cooled transmitting tubes. Your molded sleeve concept can probably work with the right material.
On the other hand, most of the heat from a tube is radiated, not conducted. Therefore, cooling the glass won't help too much. You have to cool the electrodes (plate) inside. Really big power tube give you metal contact with the electrodes (forget the glass). There is little thermal conductivity between the glass and metal, especially with a vacuum in the middle. What you don't want to do is surround the tube with mirrors (which a number of amplifier makers do). The mirrors will reflect the radiated heat right back to the tube, forming an oven. Black surfaces (or none at all) work best.
If you use a fan, aim it at the base of the tube. That is where you need the convection or airflow. Also, make sure the tube isn't radiating all that power into other chassis components.
As far as soft start, I believe that is where your choke rectified heaters come in. Such an arrangement is extremely gentle.
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