post war conventional locos

Not directly.  You need to have a remote control power source that the command base/CAB can communicate with, e.g. a modern ZW/ZW-L, TPC, or a PowerMaster.  The command base and CAB can only directly control Command equipped loco's.  You can by command boards (and sound) if you chose to upgrade the older loco's to command control but that's a different story.

The short answer is yes but as Chuck says you need another "brick" that will allow you to vary track power the way you would with a conventional transformer.

Answer is yes and here are some details: I have a ZW-C, Command base, and CAB1.

 I can run any track with the cab1 either conventional or TMCC. (I have 3 tracks)

  There are other combinations of hardware that will do the same thing but this is what I have.  Don

I understand that the conventional train's speed is controlled by changing the voltage. I have a post war zw transformer I use to power the track for the conventional train. Can the Cab1 vari the voltage from the post war zw to control the conventional trains?

Not without a TPC or PowerMaster.  You would set the "transformer" for max voltage and put the control device between the transformer and the track.

Ok, if I wanna control two post war trains, each on a different track, I would need two tpc's.

Unless you want them to do the exact same things at the exact same time, yes.