[GreenKeys] History - Why voltages and frequencies are chosen (5v & 3.3v logic, 6.3v filaments, 120/220 VAC, 50/60Hz etc)

[Charles Ring]

On 11/21/2012 1737, Paul Wills wrote:
> Actually it's 16 2/3 Hz.  It's exactly 1/3 of 50 Hz. It allows a 
> simple 1 to 3 ratio of poles on each end of the MG set.

I think the only mystery remaining here is, why 6.3 volts for tube 
filaments, and i will add why also 5 volts for rectifier filements?
>
> Amtrak still runs 25Hz from the east end of Sunnyside Yard (New York 
> City) and Washington, DC as well as the Harrisburg line. SEPTA (The 
> Philadelphia commuter authority) also runs 25 Hz but mostly because 
> they are the "tail" being wagged by the Amtrak "dog."
>
> They're committed to it for the long term as most of the rotary 
> frequency changers have already been replaced with solid state units.  
> (There are also two, I believe, hydro-electric generators on the 
> Susquehanna river at Safe Harbor dam.)
>
> PDW

Are the 25 cps areas also still 11,000 volts?


-- 
*Charles Ring W3NU*
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