As the [man page] for [tclvars] mentions, one can examine [TBC] by
generation of [Tcl] with '''TCL_COMPILE_DEBUG''', followed by 
execution in a run-time context with at least one of [tcl_traceCompile]
and '''tcl_traceExec''' non-zero.

[DKF] provides a different formula, relying on '''--enable-symbols=compile''', 
in this
[http://groups.google.com/group/comp.lang.tcl/msg/1204437fb12839e1]
[comp.lang.tcl] posting.