[GreenKeys] Loop power supplies

[Jack]

United Press used a small transistorized constant current gadget. It might been the NR unit. Maybe we could get some PC boards made up? We’d have to find current suitable transistors. 
Jack K2TTY


Sent from my iPhone

> On Mar 3, 2018, at 6:05 PM, Sheldon Daitch via GreenKeys <greenkeys at mailman.qth.net> wrote:
> 
> 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
> 
> 73
> Sheldon
> 
> 
> 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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