What on earth is this?

Over the weekend, I helped my brother clear out his loft, because they are moving home. In it, we found this ancient bit of valve equipment, which we have totally failed to be able to identify.

Any ideas?

Its heavy and a peek behind the back board looks like some seriously big tubes, but interestingly very little in the way of ventilation.

The big control in the middle is a 3 position switch labelled 200/400, 300/600, 1000/2000

Its made by Phillips - and both ends are the same, each with a big knob and a small knob. 

One big knob changes the dial setting labelled 'S' and the other the dial labelled 'P'

Its very very odd.

Any help identifying this would be much appreciated.