[GreenKeys] "Mystery" M28D

[Duncan M. Brown]

The AWA Museum has been offered a Teletype model "28D".  In looking on the
Internet for info on a "D" model (never heard of it before), the only place
I found any detail about it is on Nick's Virhistory site
http://www.virhistory.com/ham/rtty-05.htm  where he asks about it.  
 
Nick has pictures & differences on the above site, so I won't repeat it
here.  Anyone Know what it's modifications were for??
 
Thanks, 
 
Duncan Brown, K2OEQ
 
Chief TTY operator & repairman
AWA Electronic Communication Museum
http://www.antiquewireless.org/