Phenomenology of the Top Mass in Realistic Extended Technicolor Models
  Extended technicolor (ETC) theories typically require ETC gauge bosons lighter than of order 1 TeV, to perturbatively generate the $t$ quark mass. We point out that explicit models of $t-b$ mass splitting also typically contain additional TeV scale ETC gauge bosons transforming in the {\it adjoint} of technicolor, leading to large weak-isospin-breaking effects observable in the $\rho$ parameter. Viable ETC models may thus require a lowest ETC scale of order 10 TeV, with relatively strong and finely tuned couplings to generate $m_t$. Such models do not generate observable corrections to the $Zb{\bar b}$ vertex. 
Thomas Appelquist, Nick Evans and Stephen B. Selipsky