Great thread Tony, sorry bit late here as I am satisfied with my audio since the mid eighties.
Always bought as non working as I couldn't afford GWA kit at the time.
I bought a non working Leak TL50+ and contacted Leak for a cct diagram, an A4 envelope arrived stuffed with one of every Leak TL / Stereo Amp and Pre / Tuner diagrams available that they had FOC.
A lovely binder file I made to keep them preserved.
In the early days of Hi-Fi some makers printed the cct diagram on the base plate of amplifiers ect, it stopped I guess because they got worn away.
In the later eighties some high end makers would conceal the transistor device number to protect copyright.
Idiots, in the know people can remove and plot the characteristics of the device and find an alternative.
It applies today with obsolete devices, you can always find a usable alternative
How many would be able to change a mains plug if the wiring diagram wasn’t made available? Would denying the end-user this information make the world a safer place
When I did a C&G electronic servicing course at college, we were given a task to wire up a 13amp plug.
We all failed because when you tug the cable away from the plug the earth should remain connected when the live and neutral give way.
The technique is to wind the earth lead around the screwdriver shaft once to extend it making it the last connection to break away in a failed strained cable situation.
Hope this helps?
Thanks for all the useful youtube vids, I wish I wasn't retired, too frail at my age.