[GreenKeys] Current Loop Converter

[Ralph Mowery]

----- Original Message ----- 
From: <WA5CAB at cs.com>
To: <ehorne at speakeasy.net>; <greenkeys at mailman.qth.net>
Sent: Friday, December 11, 2009 11:59 AM
Subject: Re: [GreenKeys] Current Loop Converter


> Bill,
>
> I'm not absolutely certain about 28 Series units, although I think they 
> are
> all strappable for either current.  Most 14/15/19 sets only run 60 ma, as
> most machines were shipped with the large almost cylindrical pulling 
> magnets
> and magnet assembly.  There is an optional holding magnet assembly that is
> switchable between 60 and 20 ma.  It isn't common.  I think I've only ever
> had two machines with it.  The magnets on it are smaller and almost square
> cross section.
>
>

The 14/15/19 sets can be ran at either 30 or 60 ma.  I am not sure where or 
how the 20 ma got into the discussionof that series.  I know 20 ma is common 
in computer circuits.

I have not worked with the 32/33 series of printers. From what I have read 
they operate with a 500 ma internal loop and the internal circuit does the 
conversion.  Maybe they will operate on a 20 ma circuit ?

It does not mater if you have the holding or pulling magnets in the 15 
printer.  You put them in series for 30 ma and parallel for 60 ma.  Also 
they have to be phased correctly.  If not you get a weak magnet effect.
Most 15 printers need to be set for 60 ma as this puts less effective 
inductance in the circuit and you get less distortion.  This is a big help 
in the radio circuits.

The holding magnets were more desirable due to having less inductance.  I am 
not sure if there is any other reason for them or not.

I have not worked with the 28 series either, but did a quick look in a RTTY 
Journal.  They mention a local loop within the machine.  Also is a mention 
of hooking directly to the magnets and eliminating the other circuits in the 
printer.

73 de KU4PT