Reason why RCA designed AC/DC sets

[Jonathan]

I have a couple radios from RCA from the 30s and 40s that have SW and BC bands and have no power transaformer. Why did RCA come out with these and not seal up the back so wandering hands or the inexperienced repairman wouldn't touch it?

Were these sets made for customers that couldn't afford transformer sets or compatibility with both AC and DC? I prefer transformer sets as I don't have to use an isolation transformer all the time. I guess multiband radios were expensive and using a live chassis kept the cost down.

Thanks.

Jonathan