[GreenKeys] Modem with 20mA current loop interface

[Geoff]

On Tue, 16 Dec 2014 07:41:31 am Jim Haynes wrote:
> On Mon, 15 Dec 2014, drlegendre . wrote:
> > What other 20mA 'levels' exist, and what differentiates them?
> > Would the 12V / 470-600R loop used with many simple level converters be
> > considered low-level 20mA?
>
> Yeah, what I mean is that the M32/33/35 machines use electronic selector
> magnet drivers and the input to those is 20 or 60 ma but at low voltage,
> like 20 volts.  The older machines, M14/15/28 have the selector magnets
> brought out, not run through a solid state driver, so they require 60 or
> 20 ma at typically a high voltage like 120V and generate inductive kick
> when the circuit is opened.  A very few of them have solid state drivers
> incorporated so the input loop can run at low voltage.  And you can use
> less than 120V with a more complicated driver circuit, or if you have
> perfect signals to begin with.
snipped

Hi Jim et al,

	I have several model 32s that are on my ""to do" list. I have the circuit 
diagram for the select magnet driver but it does not give the details of the 
semiconductors.. The transistors in particular will be important for anyone 
(like myself) wanting to reproduce the driver circuit.

	Is anyone able to supply the details of these transistors? Even the original 
would be enough to start the process.

	Any help/information will be gratrefully accepted.

Cheers,

Geoff.