![](baseb4a.jpg)
This base probably originated in the late 1940's or early 1950's. The designation B4A has been taken from its use on the data-sheet for CV398 and an STC catalogue.
The RCA data-sheet for the 715C numbers the pins clockwise from the notch, the CV register numbers the pins as shown above. We have adopted the UK numbering.
![](baseb4a1.jpg)
The ceramic B4A base with bar to fit into the notch and locking lever. od 82mm, id 46mm.
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