An amazing find. I'd never heard of 2" IO. Like the OP I thought they only came in 3" and 4.5" diameters.
Quote:
Originally Posted by BrianSummers
In the early days the BBC would not buy tubes but had them on "rental" and returned them after a certain number of hours of use.
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This was certainly true for the pre-war Emitrons. The interesting question is whether this rental arrangment was at the insistance of the BBC or the tube makers.