[davemc]

There is an article on the restoration of these devices, but I don't remember where I saw it! It might have been in an AWA publication. The article also described the appropriate solution for the electrolyte. The problem is cleaning out the residue without having to remove the metal caps. Here is part of an article on how they work.

http://www.thorneyhill2.freeserve.co.uk/metalrec.html (no longer works)

In 1920 it was already common knowledge that rectification of AC could be obtained by passing current through a circuit made by immersing an aluminium plate and a lead plate in a solution of ammonium phosphate or sodium borate. It had been found that when this was done a layer of oxide formed on the aluminium plate which then acted as a "valve" to the passage of alternating current in the circuit. Not only simple half-wave rectification was possible but full wave rectification was also achieved through the expedient of using two aluminium plates with the lead plate in between. For these "electrolytic" rectifiers, it had been found that some 60% efficiency was obtained, the other 40% being dissipated as heat. Future development had been forecast at the time, through cooling the aluminium plates, but because mercury vapour rectifiers were then the better option, the impetus of further experimentation leading to new devices was not a priority.

I tried unsuccessfully to restore one of these Philco supplies. Mine was a combination A and B eliminator. The large A rectifier was missing (really a wet-cell charger). The supply originally had a 6 volt wet cell inside. I could never get the cells cleaned out through the small hole in the top. I may jump at a more complete unit in the future and try again.

You see single cells listed on eBay all the time - usually listed as BATTERIES.