A spherical shell model for turbulence, obtained by coupling N replica
s of the Gledzer, Okhitani and Yamada shell model, is considered. Cons
ervation of energy and of a helicity-like invariant is imposed in the
inviscid limit. In the N --> infinity limit this model is analytically
soluble and is remarkably similar to the random coupling model versio
n of shell dynamics. We have studied numerically the convergence of th
e scaling exponents toward the value predicted by Kolmogorov theory (K
41). We have found that the rate of convergence to the K41 solution is
linear in 1/N. The restoring of Kolmogorov law has been related to th
e behaviour of the probability distribution functions of the instantan
eous scaling exponent.