[GreenKeys] Western Union Ticker-5A Stock Quotation Machine

Tue Apr 17 20:14:14 EDT 2007

Hi

People have been running transistor based constant current loops for  
at least 40 years. I built my first one about 35 years ago. Even with  
a constant current you need at least 60 volts to get a reasonable  
distortion level on 60 ma magnets. With 20 ma magnets (series  
connected) you would need a lot more voltage.

I have the data on the coils sitting around here somewhere. Going  
from memory 4 H comes to mind for the inductance of each magnet in  
the pair.

Bob

On Apr 17, 2007, at 7:51 PM, Brooke Clarke wrote:

> Hi Bob:
>
> I understand from reading about telegraph sounders the T=L/R time  
> constant.
> If a low voltage battery is used (choosing battery voltage = (coil  
> R) * (coil pull in current) then the speed of operation may not be  
> fast enough.  Just increasing voltage (and running the coil at  
> higher current and adding heat) does not speed it up.  But adding a  
> series resistor and adding enough voltage to get the coil pull in  
> current) does speed it up.
> http://artifaxbooks.com/sounders.htm
>
> I think if a current source is used the R value approaches infinity  
> and you don't need a lot of voltage. Just the coil voltage drop +  
> current source voltage drop and a little margin.  In my case that's  
> under 5 volts.
>
> I don't understand your comment "Regardless of weather you use a
> > constant current loop or a resistor".   Voltages around 100 are  
> common for driving RTTY machines in the present day, but don't know  
> if it's really needed, or is a carry over from the old days.
>
> I have some H-Bridge ICs on order.  These are similar in concept to  
> the bridged stereo amp, but simpler and with logic level inputs.  A  
> 3-terminal voltage regulator IC and a resistor makes a good current  
> source.
>
> What's a common input R and L for a teletype machine?  Has anyone  
> tried a current source drive?
>
> Have Fun,
>
> Brooke Clarke, N6GCE
>
> w/Java http://www.PRC68.com
> w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
> http://www.precisionclock.com
>
>
>
> Bob Camp wrote:
>> Hi
>> One simple way to drive a pure polar coil is to put it between a   
>> bridged stereo amp chip's two outputs. An appropriate resistor in   
>> series will allow you to set the current to a reasonable level.
>> The high voltage supplies normally used allow you to get a highly   
>> inductive coil "up to current" fast. Regardless of weather you use  
>> a  constant current loop or a resistor based loop you need a  
>> reasonable  amount of voltage to get the current moving fast.
>> Typical constant current loop voltages run up around 60 to 90  
>> volts.  Resistor based loops run from about 120 volts up to  
>> (rarely) 250 volts.
>> If you want to go nuts you can build a switcher along with a data   
>> delay and only have the voltage on the loop coil when you need it.
>> Bob
>> KB8TQ
>> On Apr 17, 2007, at 6:33 PM, Brooke Clarke wrote:
>>> Hi:
>>>
>>> I'm trying to bring a Western Union Ticker-5A Stock Quotation   
>>> Machine back to life.  This is the machine that replaced the  
>>> older  stock ticker machines that were under glass domes to keep  
>>> down the  noise.  I'd say that it's father was the Edison  
>>> Universal stock  ticker that changed Edison from someone who was  
>>> broke to a multi  millionaire.  It's mother was the model 26  
>>> Teletype machine since  they both use a similar, but not  
>>> interchangeable, selector cage.
>>>
>>> It's my understanding that the 26 was good for 100 CPM yet the  
>>> 5A  was good for 500 CPM.
>>>
>>> The 5A uses a permutation code that consists of 5 bits but  
>>> instead  of using a character for shift to numbers and another  
>>> character for  shift to letters the 5A uses another code bit for  
>>> this so the total  number of bits in the code is 6.  This solves  
>>> the stuck in figures  problem.
>>>
>>> But unlike teletype machines the 5A does NOT use start and stop   
>>> bits.  This is one of the things that makes it fast.
>>>
>>> The thing I'm working on now is how to drive it.  The input goes  
>>> to  a polar relay that expects to see current polarity reversals,  
>>> not  the on off keying that a normal teletype machine uses.   
>>> Testing has  revealed that it wants to see 50 to 100 ma and being  
>>> a 20 ohm coil  a little over 1 volt is all that's required.
>>>
>>> Are that circuits already in existence that will take in RS-232  
>>> and  supply the bi polar drive current?  I think that might be  
>>> more  common in the UK or Australia than in the US.
>>>
>>> Why do teletype machines typically have loop voltages in the 100  
>>> to  200 volt area?  Could these be replaced by current sources  
>>> that  have a voltage compliance a litter higher than the voltage  
>>> drop  across the input relay coil?
>>>
>>> For more on the 5A see my web page:
>>>
>>> http://www.pacificsites.com/~brooke/WU5A.shtml
>>>
>>> Have Fun,
>>>
>>> Brooke Clarke, N6GCE
>>> -- 
>>> w/Java http://www.PRC68.com
>>> w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
>>> http://www.precisionclock.com
>>>
>>> _______________________________________________
>>> GreenKeys mailing list
>>> GreenKeys at mailman.qth.net
>>> http://mailman.qth.net/mailman/listinfo/greenkeys
>>>
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