With regards the C945, I think it's the KSC 945 NPN - 60V, 150mA, 250mW 300MHz transistor. The BC174, BC182, BC190 and BC546 can possibly be used in its place. There should be others, as these are all quite common.
For the C1815 I also ended up at the 2SC1815, but there should be other, will look further.
I'm still not in the clear on the 9012, but have not really looked too hard yet.
can u teach me how you identify them? step by step maybe.. tq
im trying to simulate an electronic siren but there is no 8 ohm speaker in multisim.. how? using speaker from labview instrument but the only sound it make was a 'dot' sound.. can someone help?
Actually for the hard ones I didn't know, I just typed the number you have supplied onto google, then when I came up with something more complete, I looked it up in my component manuals.
It's difficult to teach anything else, maybe some ubber electronics pro can give you better tips.
Sorry, I have never used multisim, so will not be able to help you there.
Someone hopefully knows.