[GreenKeys] Re: Rheostat

[Peter Gottlieb]

I only need to turn off the loop current for a short time, just to get 
the data in.  I didn't mean to open it to let the machine run open, I am 
using the transistor as the keyer element.

Peter


WA5CAB at cs.com wrote:
> Well, you're correct that using an active device can wash out loop current 
> changes due to the quite large line voltage excursion you listed.  No way to do 
> that with the resistor other than by manual adjustment.  But I don't recall 
> reading why it was you needed to turn off the loop current.  Doing that will let 
> the machine run open.
>
> In a message dated 4/10/2007 12:53:15 PM Central Standard Time, 
> nerd at verizon.net writes: 
>   
>> Wow I must be a space cadet - or getting old - as I completely missed 
>> the part of the sentence after "EMP."
>>
>> My logic in using the transistor is that it serves both as a constant 
>> current device as well as the loop switch.  When I had just the keyboard 
>> in series with the magnet all I used as, in fact, just a simple resistor 
>> to set the 60 ma.  But now that I need a switch... why not "neaten up" 
>> the loop regulation against line voltage variations (105 to 130 here) at 
>> the same time.  Once I get the whole thing together I will post the 
>> diagram.  I think it does everything necessary easily, cheaply, and 
>> hopefully reliably.
>>
>>     
>
> Robert Downs - Houston
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