Early Admiral on Kijiji Toronto

[Kevin Kuehn]

I can just start to perceive flicker at 30hz using a sine wave on an LED. But the LED is only seeing half cycles. I doubt my eyes would see any flicker in an incandescent at 25hz.

[wa2ise]

Originally Posted by Eric H

Can you imagine the Flicker of light bulbs at 25 Hz?

I've seen it. Back in the early 60's, parts of the New York City subway system used 25Hz. Their light bulbs lighting the stations did flicker. An oddity of the human eye is that the brighter the light source is, the higher the frequency you need to avoid the perception of flicker goes up. The rest of the station didn't seem to flicker as much as the bare bulbs themselves did. As the rest of the station hits your retina as a lower bightness level. Also 3 phases of electric supply would also smooth things out.

You also see this effect on 50Hz TV displays (PAL) vs 60Hz (NTSC) at higher brightness settings on CRTs.

A power transformer designed for 120V@25Hz in theory will be happy at 240V@60Hz. All the secondary voltages will be twice the rated voltages. One limitation is how good the insulation is on the secondary used to make B+.

[old_coot88]

Originally Posted by electroking

Has anybody actually seen the flicker at 25 Hz with incandescent bulbs?

Absolutely.
This was in Roosevelt, AZ in the 60s and early 70s, during visits to the local bait & tackle store. The bulbs i saw were clear glass, dunno if the flicker woulda been diminished any if they had been frosted glass.
Conversion to 60 cycle didn't come until 1973. Here's a bit of skinny on the frequency standardizarion project..
https://www.srpnet.com/gallery/trd/1971.aspx

[Penthode]

Some may recall my RCA CTC5 bought in Toronto was converted in Montreal for 25 Hz power. It had a separate chassis added underneath which sported a heavy B supply transformer and the original chassis mounted transformer was changed for filaments only. The modigivcation added about another 25 pounds to an already heavy set.

Old timers including my Dad remembered the flickering bulbs. Interestinglyly people got used to it: my Dad emigrated to Canada in 1948 and he said the flickering lamps in Toronto initially gave him a headache. But after a few months he got used to it. Note that even though the frequency is 25Hz, the bulb flicker rate was 50 Hz.

I believe Toronto switched to 60Hz around 1958 when there was a major 25Hz generator failure.

Incidently the Tesla standard was 60Hz and he had to face opposition at Niagara when the engineers there wanted 16Hz. The compromise was reached at 25Hz in 1893. The last 25 Hz William Rankine generation at Niagara closed only in 2009.

Terry

[nasadowsk]

Amtrak's Northeast Corridor is still 25hz below the phase break on the Hell Gate bridge approach. I remember in college seeing E60's in Penn Station, and yes, their number boards and all had a noticeable flicker to them. HEP is 60Hz, but I suspect there's a strong 25hz harmonic riding on it because you can see a slight flicker on older Amfleet cars once you change from 60Hz to 25Hz power.
They convert it at a few places, notably Metuchen, NJ. I have an article on SEPTA's 25Hz converter at Wayne Junction - ASEA built it in the late 80's and it was quite an interesting beast. Even today, listen closely to a SEPTA regional train, and you can hear a slight rumbling as they pull out of the station.

[nasadowsk]

Originally Posted by Penthode

Incidently the Tesla standard was 60Hz and he had to face opposition at Niagara when the engineers there wanted 16Hz. The compromise was reached at 25Hz in 1893.

16 2/3rds is still a standard frequency for RR traction in Germany, Austria, Switzerland, Sweden, and a few other countries. 25Hz became the standard in the US and is still used (see above post)

[old_coot88]

OOPs! Duplicate post.