Hewittic 150/6G grid-controlled Mercury Arc Rectifier, serial number 35161.

This is a 6-phase device, 150A rating with grid control.

It measures 600mm high by 530mm diameter.

Further information on these devices can be found here.

A view of one of the anodes - there are six of these equally spaced around the bulb. On the right is the control grid.

Closeup of one of the control grids.

A view down to the mercury pool. The starting electrode can be seen. This electrode is moved by an external solenoid acting on a small magnet which can be seen below.

Another general view of the device. In this picture the starting electrode connection can be seen running straight out sideways between the two anodes on the right, and one of the two exciter anodes (see below) can be seen at the bottom.

Top view.