reverse on/off switch

[MacAttak]

Closing the switch is effectively the same thing as soldering the base and emitter together. It doesn't matter what else is going on in that circuit - if the base and emitter are connected together, the transistor cannot be "on".

[duskglow]

Thanks all, I really hate asking stupid questions, but there are some pretty big gaps in my knowledge that I need to plug if I want to go anywhere with this.

[hlavac]

Think of NPN BJT like this:
Base-Emitor is a diode in forward direction (anode at base, cathode at emittor).
Like any diode it develops a voltage drop across it before any significant current will pass thru it.

Collector-Base looks like another diode (anode at base, cathode at collector).
This diode is normally reverse biased (current could flow freely from base to collector).

Any current passing thru base-emitor diode will allow up to beta-times more current to pass from collector to emittor. Collector-emittor voltage drop will change to allow this current to flow, subject to minimal voltage drop of about 0.2V between collector and emittor.

PNP looks the same but the diodes are reversed (cathodes at base) and base current flows in the opposite direction (out of the base)

[lewis]

Think of PNP BJT like this:

You mean NPN

[hlavac]

yes NPN, typo Fixed