Of course DC current was available in places other than ships.? For instance large parts of Manhatten had DC until fairly recently.? ?You had to have an AC/DC receiver to work there.? However most AC/DC sets were simply economy models to eliminate the transformer.? Having said this both Radiomarine(RCA) and Mackay made two versions of some receivers : an AC version, for use at land stations and on ships with AC mains,? and an AC/ DC version for use on ships with only DC power.??

Because of the S-40’s? leading to the S-77’s and S-52 and S-51 I looked at these older units ?
the s-22 , and 22R are called marine by Dachis , and? they do LF [low frequency] or,LW [long wave] as well as higher frequencies, and they can be run on DC as well as AC. so i looked at bama manuals for more info and found..
the S-22R and then S-22, are both called marine by Halligan, and both have a LF or LW band and are normally 110 AC/DC

Just for the record, re the S-51, I previously said? “it has the LM marine band”….that should be ?.. a LF marine band” or maybe LW.
Copied from the s-22R manual--------

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Looks to me that you could run into 220 vdc? version that appears the same model No

?

Now here is an interesting thing..for another day...

Copied from the s-22R manual---------

..there appears to be no octal socket for DC

Copied from the s-22[no R] bama manual maybe a riders appendix---------