This
gear drive is mounted on the front of the receiver. It is easily removed
by unscrewing 3 screws. Lots of hams have removed the drive so that they
could have access to the variable frequency tuning cap. Mine is missing
from this receiver.
This gear came from a MN-26 C and fits my receiver a DB-10.
Coupling, it may be missing but I can make one.
The small box and switch on top of the control head are used for remote control of the receivers loop relay unit. The relay unit is mounted on front of the receiver and is nothing more than an enclosed relay used for selecting either the loop or the wire antenna.