Model 33 wiring complexity

Ethan Dicks ethan.dicks at
Wed May 10 14:12:15 CDT 2017

On Wed, May 10, 2017 at 2:22 PM, Paul Koning via cctalk
<cctalk at> wrote:
> I'd put it this way:  For teletypes, the receiver is predominantly an inductive load.  And it wants a fairly short rise time, so you pick the time constant you need, which gives you R, which in turn gives you the needed drive voltage.  And that works out to be a fairly high voltage in a lot of cases, especially with the older machines with 60 mA loop current.  The needed loop R is almost entirely the series R; the receiver coil adds very little to the total.

I'm restoring a Model 19 teletype (5-level Baudot). The current loop
is 60mA, and uses 120VDC for the loop.  Typical of the class.


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