[GreenKeys] Current limiting

[Sheldon Daitch]

Northern Radio made their Type 238 Loop Current Control unit, exactly for
this situation, the Model 1 version was for 60 mA loops, the model 2 version
was designed for 20 mA loops.

It was accompanied by the Type 242 Models 1 and 2 shelf unit, 9 slots 
available
for the Type 238 Loop Current control modules.

Functionally, it is a self powered current limiter circuit, with a 
non-linear
bridge driving an error amplifier driving a pass transistor as the current
regulator.

If there is any interest, I can PDF pertinent pages from the manual I 
have and
send to anyone who desires.  Bear in mind this is a 1959 design, so the 
parts
used in this unit will be a bit dated.

73
Sheldon

Don Robert House wrote:
> 25-50 watts in series with a fixed resistor for shorter loops.
>
> Don
> K9TTY
>
> I can send images if someone wants them.
>
>
> On 19 Jan 2009, at 6:09 PM, Bob McConnell wrote:
>
> Larry Tighe wrote:
>   
>> Howdy Folks,
>>
>> what limits the current in the WECo power supply under the TTY  
>> machine to 60
>> ma.?  Is it the ferro resonant?  This p.s. is very quiet and I don't  
>> have a
>> print on the box....model 12 power supply I think.
>>
>> lar
>> Larry
>> www.antiquetelephone.com
>>     
>
> Hi Larry,
>
> The circuits I was familiar with all used a big honking rheostat in the
> loop. Usually the loop supplies were about 135V DC with very low
> impedance. The rheostat was adjusted to 60 ma each time we added or
> removed a machine from the loop. I believe they were 5 watts each, but
> they may have been more.
>
> Bob McConnell
> Ex-RM2 USN - NFIT, NLM
> N2SPP
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