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External Anode Tubes

February 9th Fact-of-the-Day

All vacuum tube elements were encased in a tube in early designs. That practice continued for most low-power tubes. However, high-power tube designers realized in the 1950's there is no need to encase a tube's anode inside a tube and not doing so has important advantages. An anode normally dissipates much more heat than all the other elements combined. It is difficult to get rid of that heat if an anode is inside a vacuum chamber, but it is relatively easy if an anode is also the outside surface of a tube. Output lead inductance can be much smaller, because a large conductor can connect directly, rather than via a small diameter lead that penetrates a vacuum enclosure. External anode tubes can be smaller, both because more heat can be dissipated and because there is no space between an anode and a vacuum container. ©2005 Martek International All rights reserved.


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