Another 10BP4 on ebay...

[nasadowsk]

Yet another 'extremely rare' 10BP4 on ebay. This one's not new in box. These things pop up constantly, it seems.

Ok - so, big question - how come there are zillions of these things *still* floating around? I've seen plenty of unused 10BP4s, a good number of them new in box. Did RCA overproduce, not anticipating a shift towards larger screens that happened relatively quickly? And, weirdly - it was listed as in production even into the late 50's, in RCA's tube manual.

Wha'ts the story on them?