Thanks Guys - I tried swapping PB1 & PB3 (only one needs to be PWM) and it works fine on PB1. Odd that - I'm sure I checked the datasheet when I was planning this project.
Anyhow, tone works on PB4 (&PB3) - I think that may have been down to my old version before - and PWM works on PB1, which will do me fine.
I don't understand how tone works on PB3 if PWM doesn't, but maybe that's a cunning interrupt-based version.
Thanks for your help.
Ugi