In the vacuum tube era, a tube (e.g. 6V6) was usually produced by several
manufacturers. I am not sure of how things actually went, but I would say
that a manufacturer initially designed the tube and put it on the market,
and subsequently other manufacturers "copied" the tube. But how did they
actually copy it? Just by reverse engineering (e.g. measuring dimensions and
distances among electrodes)? Or instead the original manufacturer published
the detailed tube design so allowing others to produce it? The first option
seems more likely to me, as manufacturers should have little interest in
helping others to replicate a tube.

The same question applies to solid-state devices, but in that case I would
expect that reproducing a device having (almost) the same characteristics
through a reverse engineering process would be very hard, if not
impoossible.

Does any one know how things go in practice?

73

Tony I0JX
Rome, Italy