I read that in 1960s everything worked on DC. Why is that? DC is expensive than AC!

I don't know where you read that, but most power circuits in North America have used AC since the 1920's.

A lot of the earliest AC systems were run at 25 Hz, but that was phased out in favor of 60 Hz from at least the 1940's.

Regards,
Brian

Mike,

I'm afraid what you read is totally incorrect.

Here in the U.K. we had old DC supplies in some areas which were still in use into the 1960s, at which time they were converted to AC.

I don't know the details of the conversion of old systems in America, but I would guess the 1960s is more likely the time when the last remaining DC sevices were changed to AC, as here.

P.S. On both sides of the Atlantic, many AC systems were installed way back in the 1890s. There was a long battle at the time between Thomas Edison (DC) and George Westinghouse (AC).

[This message has been edited by pauluk (edited 11-30-2001).]

They're correct, what you read is wrong. What you may have read, and was the subject of a recent thread on this forum was about the 5 wire system. Some of the older wiring, CHANGED OVER TO AC IN THE 30's, existed in the older sections of Washington, DC (and I'm sure other old towns) for a long time. I was involved in the early 70's with conversions of these old systems, but I don't think many were around long after that.

Just another possibility: Are you thinking of radios, TVs etc. which were advertised as AC/DC models?

These were very common up to the 1960s (and into the 1970s for some TV sets). It didn't mean that all the supplies were DC, just that the sets didn't use a mains power transformer and could be run on AC or DC mains supplies.