[GreenKeys] 60ma loop supply

[Bob Camp]

Hi,

Are we talking about six devices in one loop or six seperate loops?

In the first case you have 60 ma and a lot of voltage. In the second case
you have 360 ma and not quite as much voltage. Obviously there are various
configurations in between the two. A lot also depends on weather you are
running 28 or later stuff with internal loops or earlier stuff with external
loops. For the moment let's assume it's 15 and 19 stuff with external loops.

Here's one of many ways to go:

1) put each set of magnets on it's own loop supply. Either put in a dropping
resistor or a solid state (constant current) loop. Key each loop with a
transistor driven off of a opto-isolator.

2) set up a couple of loops for the switch contacts. Since these no longer
have to switch magnets the current and voltage can be fairly low.

3) plug the opto-isolators from the "magnet" loops in to which ever switch
contact loop they happen to want to run off of.

The advantage of doing it this way is that each gizmo with a magnet in it
(punch, printer, what ever ...) is more or less self contained. All the high
voltage keying stays inside the cabinet if you do it right.

The low voltage loops probably only need to be about 24 volts and a couple
of ma. A more or less standard 24 volt 1/2A supply and a couple of 6K ohm
two watt resistors should do just fine.

If you can still find them MJE340 transistors (I *think* that's the number)
used to do an ok job both for magnet keying and for the constant current
part of the loop.

I don't know if this is heading in the right direction or not. If it is and
it's not clear let me know and I'll elaborate.

    Take Care!

        Bob Camp
        KB8TQ





----- Original Message -----
From: "Gregory W. Moore" <gwmoore@moorefelines.com>
To: "Greenkeys Reflector" <greenkeys@mailman.qth.net>
Sent: Monday, September 09, 2002 1:59 PM
Subject: [GreenKeys] 60ma loop supply


> Does anyone have a good schematic for a 60 ma loop supply capable of
> supplying up to 6 loops? I use the old '72 ARRL Manual one for a single
> loop, but it current limits thru a dropping resistor. Since I am now
> acquiring a proper patch panel, I should have a supply that will carry
> multiple teletypes, both for test and operational purposes.
> 73 es tnx de Greg WA3IVX
>
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