[GreenKeys] model 15 20/60 switch

[John, W9DDD]

Re: the M28, yes has a hard to get to terminal strip accessed from the 
bottom of the LESU.   I remember the switch on the TT-76.  My GRC-46 was 
missing the TT-98 for the whole year I was assigned to it.  So I don't 
know about it. Never saw TT-4 while on active duty.  But you have 
explained what at the time seemed to be a strange way to label the switch.


On 11/15/2024 11:34 AM, Duncan Brown wrote:
> The 60 ma loop comes from the DC telegraph circuits which could be 
> miles long.  In the 1940-50s, when more TTYs were used with voice 
> circuits (telephone modems & radios), the distance to the modem or 
> radio converter (TU) was measured in feet, not miles, and a lower loop 
> current could be used.
>
> All the Kleinschmidt models (designed for the military, starting in 
> the late 1940s) had easily accessible 20/60 ma switches. The switch on 
> the TT-4 was labeled "DC LINE / VOICE FREQ LINE"
>
> In the M28 line, there was typically an "Electrical Service Unit" 
> (ESU) which contained a polar relay that isolated the selector magnet 
> from the external line.  Since the SM was on an internal loop, it did 
> not need to easily switched between 20 & 60 ma.  I'm not as familiar 
> with the M28 line, but I think there as probably a wiring choice on 
> the terminal strip on the rear wall for the 20/60 ma choice.
>
> Have fun,
>
> Duncan
> K2OEQ
>
>
>
> On 11/15/2024 12:07 PM, Tom Hunter wrote:
>> W9DDD,
>>
>> I have a holding magnet 15 with a 20/60 mil switch. So they did 
>> indeed put them on some 15s.
>>
>>
>> Tom N3CRK
>>
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>
>
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The above comments or recommendations are SWAG. Use at your own risk.

John, W9DDD