[GreenKeys] Loop power supplies

[Sheldon Daitch]

Here is a link to the Northern Radio Company's loop current control manual:

http://www.tmchistory.org/NorthernRadio/Manuals/ib_238-1-2_4_8_66.pdf

73Sheldon

      From: Jim Haynes <jhhaynes at earthlink.net>
 To: Ralph Mowery <rmowery28146 at earthlink.net> 
Cc: 'Green Keys' <greenkeys at mailman.qth.net>
 Sent: Saturday, March 3, 2018 11:36 AM
 Subject: Re: [GreenKeys] Loop power supplies
   
On Sat, 3 Mar 2018, Ralph Mowery wrote:

> 
> I and others have tried it, and 24 volts and under does not work even on
> short loops ( like maybe 5 or 10 feet of wire)  with machines like the model
> 15 printer.  It really needs more than 50 volts to do the job, close to 100
> or 150 volts to really work well.
> 
I haven't tried it, but there are circuits that use the "constant current"
properties of a transistor rather than a fixed resistor, and are said to
give equivalent results with lower voltages such as 48V.  For instance
QST, Jan 1972, p. 40.  Maybe someone who knows how can do a SPICE
simulation to compare such a circuit with a plain resistor.

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