[GreenKeys] TTY Ribbons

[pdwills at cedarknolltelephone.com]

Actually, it was a carry-over from the old Edison DC days. 
Since DC was not easily transmitted long distances, and
local generating plants were not cost effective, power was
distributed around the city as 3 phase 25 Hz.  Rotary
converters were used to produce the DC for local
"consumption."

When the local DC service was phased out, all that was left
was the transit facilities which still converted the 25 Hz
current to the DC required to run the system.  (Some hotels
and commercial buildings also used DC for elevators and
other "infrastructure.")

I believe that the 25Hz was retired in the 1980's and the
remaining DC service only a few years ago.

I have been in the Amtrak substations where the lighting was
powered from 25Hz power.  The flickering was quite
noticable.

PDW

----- Original Message Follows -----
From: "Larry Tighe" <larryradio at att.net>
To: <Til128 at aol.com>, <greenkeys at mailman.qth.net>
Subject: Re: [GreenKeys] TTY Ribbons
Date: Wed, 10 Aug 2011 10:15:09 -0400

> Did they flicker because of 20 cycles?  If so, why and
> where did 20 cycles  current come from?
> 
> lar
> ----- Original Message ----- 
> From: <Til128 at aol.com>
> To: <greenkeys at mailman.qth.net>
> Sent: Wednesday, August 10, 2011 10:11 AM
> Subject: Re: [GreenKeys] TTY Ribbons
> 
> 
> > light bulbs were left hand threads to prevent theft.
> >
> > True!
> >
> > TT
> 
> 
> 
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