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

[Brooke Clarke]

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
>>
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>