You were correct- the regulator is a STK730-020. I just replaced that,
and also found a service bulletin that recommended replacing the HOT
(Q551) and two ceramic caps (both are 2.4K/3W).

So, I replaced everything, and as bad luck would have it, I'm no longer
getting high voltage when I turn on the set- the replay clicks on,
however the tube does not fire up. I'm going to retrace my steps to
night and see what possible could have gone wrong. Arrrgh.

Sean