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DuMont was building radar and CRO tubes for the war effort. Most of these tubes are just P4 versions of those same tubes. I have a collection of in-house datasheets with developmental numbers from '44 or '45. It's easy to match the 12JP4, 15AP4, and 20BP4 to the developmental types. They also pioneered the lackluster 7EP4 (rapidly displaced by the 7GP4/7JP4). Some of the developmental types died off however. It's interesting reading.
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