I want to set up TMCC for use in conventional mode. I know that I need the CAB-1 controller and a Powermaster, but do I need the TMCC base?
NO.
As long as you ONLY use powermaster, no, a command base is not necceary.
If you want to use any of the other TMCC remote control accesories, such as SC-2s, TPCs, ASCs, etc, you do need the command base.
This is probaby your cheapest solution to a walk around throttle. You should be aware of issues with the wave from output of the PowerMasters. The Powermasters use a chopped sine wave that can cause some early QSI and PS-1 locomotives sound systems to misbehave or shut down. This is not the case for Lionel’s own sound boards and the normal bell/whistle/horn triggers found on non sound equipped locomotives. If you don’t have any engines that fit this criteria or you don’t mind killing the sounds you should be fine.
There was a vendor that made bi-polar capacitors that could be wired into the track feeds to provide enough of a roll off of the chopped sine wave to fool the QSI/MTH boards into working. I don’t know if these are still available.
BTW, the CAB-1 and PowerMasters predate the rest of Lionel’s system. The command base and LioneTech reverse units were introduced about a year after the CAB-1 and PM’s.