[Milsurplus] ER65

[Michael A. Bittner]

I picked up this little Swedish ER65 regenerative receiver at a local swap meet.
https://www.dropbox.com/home/ER65
It is meant for monitoring the old 500 kHz emergency frequency and is well described in the RADIO MUSEUM web site.
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My question is: What is magic about 65 Volts DC for its power source?
Was this a standard power source on some ships or shore stations, or did it require an external power supply?
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Mike, W6MAB