[captainclock1988]

That's one of the Electro brand battery eliminators, there are two basic models, one has a 1.5 volt "A" supply, the other a 2 volt "A" supply, you adjust for filament load by shorting out sections of a wire wound resistor through those screw terminals, the one that looks like an antenna/ground terminal. I can't remember but the 2 volt versions may have had a tap for 135 volts, I've only seen that model in ads so I can't say for sure. I have two of the type designed to power radios with the 1.5 volt tubes, supposedly marketed for operating portable radios, according to to the labels, likely because the "B" supply is connected directly to the power line with no isolation, so naturally a ground connection is a no-no. The one radiotvphonunt has is a Sears "PowrShftr" the design is a little different from the Electros in that it has a iron filter choke in the "B+" line, the Electro uses a RC filter with a resistor, so a little cruder, the Sears one may have also had a proper transformer for the "B" supply . 
 No I would not pay $65 for one, and did not for the two I own, the plugs are a nice feature but not essential, many 1930s farm sets had no battery plugs, the batteries had Fahnestock style clips on top for connection purposes. I think that the plug, and socket idea was for the convenience of the uninitiated so they couldn't hook the set up the wrong way, and also to avoid coming into contact with the "B+" voltage. I believe that the hardware stores, or radio shops, must have sold aftermarket battery plugs for the earlier farm sets, I have found several that had built in Fahnestock clips to connect the battery leads to, minus the solder.
Regards
Arran

Hi Arran, It seems that those old battery eliminators aren't very common (at least not as common as what radiotvphononut seems to think they are), as I looked up the Silvertone Powr Shiftr units on ebay and there were only 3 listed on ebay and all 3 of them the sellers wanted $65 for them. I'm not very good at trying to build circuits from scratch, I'm much better at working on stuff that's already built, plus I don't have anyway to make my own circuit boards (printing and etching).

I think I might be better off trying to build a power supply using a 2 D-cell battery clip and and 10 9 Volt batteries daisychained together.