[GreenKeys] Model 32s, 33s, 35s, 38s, etc. etc.

[Don Robert House]

You will recall I mentioned that the 32 was most likely a TELEX 
machine which uses line current in both directions for connection 
functions.  If the machine was NOT a TELEX it may have used a 20 ma 
local selector circuit served by a Selector Magnet Driver (SMD) Card. 
Most 33s, 35s, 38s, and 37s were designed this way.  Datasets (early 
modems) were used to convert FSK tones to operate the SMD card and 
thus the selector.

Don