[GreenKeys] Testing My Model 15 KSR

[Duncan M. Brown]

I don't know where the 20 ma came from either, but it was in use long
before TTYs where used with computers.  

All the Kleinschmidt TTYs (which came out of US Signal Corps requirements
after WWII) would do both 20 ma and 60 ma. Some where selected with a
switch and some with a plug, but they all changed the SM wiring from series
to parallel.  The 20ma choice was sometimes labeled "Voice Frequency Line"
and was used when there was only a short (matter of a few feet) connection
to the modem (TG-5/TG) or radio teletype converters. (The 60 ma position
was labeled "DC Line.) You need a lot more current to drive the signal down
a few miles of wire than down a few feet.

--Duncan





> [Original Message]
> From: Ralph Mowery <rmowery28146 at earthlink.net>
> To: <WA5CAB at cs.com>; <john at johnmcclung.com>; <greenkeys at mailman.qth.net>
> Date: 13-Apr-10 16:59:00
> Subject: Re: [GreenKeys] Testing My Model 15 KSR
>
>
> The Modle 15 series printers can not (atleast not well) run on a 20 ma 
> circuit.  Either holding or pulling coils  can be wired to run on either
30 
> or 60 ma.  If the two coils are wired in parallel then you run the
printer 
> on 60 ma if they are wired in series then you run the  printer at 30 ma. 
I 
> don't know where the 20 ma came from.  Maybe the computer printers that
run 
> on a 20 ma circuit ?
>