Thanks for the comments and suggestions, they sound good.
Wiz, I have memories of writing magazine articles and the print workers who set the lino type telling me "I have corrected the obvious mistake in your code" :-? They didn't understand logical bit wise operates and assumed it was an error.
Halley - The Darlington drivers was supposed to be a practical example of where power dissipation was the limiting factor not the devices current rating. But point taken so I think I will tackle the two power supplies first. That and split supplies always seemed to cause problems.
Nigel - Thanks, my idea was to bridge the gap between beginners and engineer and cover stuff you don't usually see so it looks like I have succeeded for you.
It would probably be good to put a link in the Playground to these but I am not sure where the best place to put it would be, any suggestions?