Can I substitute the CA3140 with something else? It appears that they CA3140 is out of production and it looks like the CA3140A has a different resistance 'setting' for its level of amplification? I see the CA3140E, but It's not clear from the docs if that is compatible with the 3140 or 3140A.
http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=679409