I agree with Carylnz with regard to the size of the tank, but not with the tetra/angel fish incompatibility: following this, for example,
http://www.thinkfish.co.uk/fish/angelfish.html, I think it's fair to say that an Angel fish will not be able to eat a tetra... I think the phrase should be 'angels *may* eat them' rather than 'angels *will* eat them', which is unfortunately just the fact of nature. Really the problem with your tank is that you would not have enough space and capacity to keep enough tetras to shoal to limit predation.