[GreenKeys] Re: Reasons for high voltge loop

[Ralph Mowery]

----- Original Message ----- 
From: "Brooke Clarke" <brooke at pacific.net>
To: <greenkeys at mailman.qth.net>; "Ralph Mowery" <rmowery28146 at earthlink.net>
Sent: Wednesday, April 18, 2007 1:33 AM
Subject: Re: Reasons for high voltge loop


> Hi Ralph:
>
> Thanks for the article.  I agree as far as it goes.  i.e. he was talking 
> about tube equipment and did not mention using a current source.
>
> It's interesting the some RTTY machines have as much as 4 H in the coil. 
> The 5-A machine I'm working with has 0.15 H and 20 Ohms, 55 ma min 
> operating current.  I'm sure it was designed that way for a reason.
>
> Have Fun,
>
> Brooke Clarke, N6GCE
>

Clarke he did mention a keying transistor.  It does not mater if it is tube, 
transistor, or just a hard contacts such as in the TD unit.  The whole thing 
is the ammount of inductance in the old equipment.  You just can not force 
enough current through an inductance fast enough to pull in the magnets of 
the older equipment that has either 2 or 4 henry coils with voltages much 
lower than about  50 volts for the 60 wpm gear.  Add two or 3 sets of coils 
in and it takes more voltage due to the time constant.  Constant current low 
voltage supplies have been tried before and just do not work very well. 
They may work for local work, but if you add in any other sources of 
distortion to the wave from , the range is so low youget errors.

For your application with .15 henry coils you can use a lot lower voltage 
and the constant current should work fine.   Some of the later modles had 
coils of lesser turns and used about 600 ma on them .  They could use a low 
voltage constant current supply.