[GreenKeys] Fwd: Re: Model 28 Motor Trivia

[Don Robert House]

Thanks to Ben for this information...


>From: K9kom at aol.com
>Date: Tue, 6 Jul 2004 14:08:55 EDT
>Subject: Re: [GreenKeys] Model 28 Motor Trivia
>To: drhouse at nadcomm.com
>Status:  
>
>The workhorse motors for the Model 28 were the synch motor, which 
>ran at 3600 rpm on commercial 60 Hz AC, and the series-governed 
>motor for everything else.   The series governed motor was specified 
>any time that the power, including AC power, was not the rock solid 
>60 Hz frequency we expect from our commercial power grids.
>
>DC motors will run on AC as well, a prime example being your vacuum 
>cleaner or blender.  I know the series governed motor was specified 
>for a couple of remote places like a Pacific Island where the 60 Hz 
>gasoline generator may or may not have been up to 60 Hz on any 
>particular day.
>
>The series-governed motor had white target spots on its black 
>plastic fan on one end of the shaft, the end facing out of the 
>machine.   With the motor came a tuning fork with a shutter on the 
>end of the fork.   To adjust the motor, you would twang the tuning 
>fork, and then look through the shutter at the fan while adjusting 
>the motor speed.  When the motor was exactly on 3600, the white 
>target spots would "freeze" when viewed through the tuning fork 
>shutter.
>
>The series governed motor cost more, and required periodic 
>maintenance like any DC motor, and the speed had to be checked 
>regularly.  But they were specified for 25 Hz, or any power source 
>from DC on up where commercial 60 Hz AC was not available.
>
>This technology was a hold over from all the earlier teletypes, the 
>14's, 15's, etc.  Some of those went out into the Canadian wilds on 
>railroad service and other North American places where the frequency 
>was not 60 Hz nor reliable.  These older machines also had 
>series-governed motors with tuning forks as an option.  So when 
>buying a teletype of any vintage, look at the motor fan.  If it is 
>black with white spots, it is series-governed.=
>
>Ben Stephens K9KOM=
>