From the Mercury, Wednesday, August 12, 1925   Radio Notes
"I was surprised to see that the American ships were fitted with the old-fashioned
navy selector, which is still in use on some of the land stations, and is a feature
of the installation of VIH."

In the radio progam Bright Sparks a WW1 operator mentioned using a receiver with
three crystal detectors - he preferred the "perikon".

The Kurrajong Radio Museum (http://www.vk2bv.org/museum/) has a "Tuner C" apparently
built about 1917, but which contains what looks like a three crystal detector.

So the POH receiver probably looked something like that.