Hey Lefty.
Thx for the lengthy response. Looks like I posted back while you were typing your last post!
When I said "minor variations"...what I was doing was changing the order of the 12V, capacitor and pin 1 on the breadboard. So for instance:
VCC-CAP-Pin 1 vs CAP-VCC-Pin 1
Technically makes no difference but only took me a second and put my mind at ease before heading back to the store only to possibly look like an idiot.
Turns out it was the cap on the output pin. They'd given me something way too small. There's a new guy at the store who apparently knows less than me!
All solved now, thanks 