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I suspect that receptacle is for a USA style power cord that was common for portable electronics back then. For example: '60 Wollensak reel to reel uses that waffle-iron style female plug on it's power cord. I expect many others did as well.

I have seen Sony reel to reels and TV's of the 60's and 70's use a 4 pin power socket a lot like on this TV...2 pins were for 12 volt DC like from a cigar lighter and the others for 110 AC...the ac cord had blank holes for the DC pins...i think Andy is right that this jack is not for ac in this case. If he did apply 110 ac to the battery pack input, maybe there was a diode in the circuit that burned up and stopped the current before it did extensive damage.

also,

Let's hope so ! That's a pretty clean set-moreso than most I've seen on De Bay.-Sandy G.

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