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Old 09-22-2016, 09:06 AM
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N2IXK N2IXK is offline
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Join Date: Apr 2011
Location: Sittin' on the "Group W" bench...
Posts: 799
Yes, they are.

In the overall history of tube development, the 8D21 was a technological "dead end", though. The complex water system needed to cool multiple internal electrodes made for constant leaks (The Kotex solution mentioned above was a typical stopgap measure to prevent lost airtime), and the 8D21 was soon replaced by air-cooled types like the 6166 which needed less attention and maintenance, and made more power with simpler circuitry (single ended rather that push-pull).

I have heard that a kit was made available to convert the TT-5 for a different type tube, but haven't found any details. Anyone out there know anything about this? It would have been a MAJOR retrofit given the physical construction of the rig.

The part of the 8D21 that did live on is the focused beam electron optical design, which was scaled up, and formed the basis of RCA's line of "Super Power" tubes which included the 5831 used in the 1 Megawatt US Navy transmitter at Jim Creek, Washington, the 6949 and 7835 used in large particle accelerators, as well as the 6448 UHF TV Tetrode. These tubes used more conventional thoriated tungsten filaments, rather than the thoria coated tantalum filament that was apparently unique to the 8D21.

Last edited by N2IXK; 09-22-2016 at 02:10 PM.
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