Thanks for your comments Gents.
Using the 57 rf pentode as an autodyne-mixer was quite common in the early 30's before the more wide spread appearance of the "octode" & "pentagrid" converter valves.
If you are interested this link explains some of the nuances and background behind the circuitry of this set.
http://messui.polygonal-moogle.com/valves/SC199711.pdf
There is a trove of articles on this site (
http://messui.polygonal-moogle.com/valves/index.html ) on vintage radio (people, repairing, restoring, collecting etc) which originally appeared in Electronics Australia, Silicon Chip & other Australian magazines from the 1960s through to this century.
The speaker cloth is a reproduction of fabric which was used by Airzone. I purchased a couple of metres of it several years ago and I've forgotten the source now. But this style cloth was used by Airzone throughout the 30s and early 40s. I've attached a photo of a 1940 Airzone Theatre which I'm currently working on for which I originally purchased the fabric but got sidetracked. LOL. The other set I used the cloth on was a Battery console Kit radio from ~1935.