N_Cook wrote:

I should have said my RCA transistor, thyristor & diode databook is 1969
(fallen apart and water/insect damaged but still useful)

Oh, I've got one of those (with thr 70W amp design that WEM used) albeit in
slightly less abused condition.

HH were well known for using 'house numbers'. The HH output transistors in
certain models for ages were simply Motorola darlington power devices in TO-3
with an HH house mark.

Graham