In article , Martin H. Eastburn
says...

Maybe a 310 was the first.

The 310 was a fairly modern scope, it had knobs that
were 454 vintage, with the black outers and red inners.

The 511 we've been discussing definitely predates that,
it used plain black knobs, one piece, and octal tubes.

The 310 used 7 and 9 pin miniature tubes.

Jim

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