Its always frustated me why the UK had to use a different system for
numbering similar things. Perhaps it's for the same reason we drive on
opposite sides of the road, hi hi hi. Drving over there frustates me so
mcuh I don't even try anymore unless there's no other choice but I do pick
up UK numbered transistors whenver I see them at swap meets, just in case
I
can use it. So far I've only found a couple!
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You probably mean European instead of UK numbering system versus the US
system.
And also there is of course the Nippon numbering system.
To my knowledge there are only few commonly used transistors with a typical
UK numbering code like the ZTX (Ferranti ?) series.


Frank GM0CSZ / KN6WH