[GreenKeys] Re: Model 15s with holding magnets...

[WA5CAB at cs.com]

My first ever M15 had holding magnets.  I cannot recall exactly from whom we 
got them but in 1962 during one of the holidays (or maybe it was Spring Break 
which might push it into 1963) someone in the group of Hams I knew at LSU set 
up the deal and my brother and I borrowed my mother's car (in those days few 
kids owned their own car) and drove from North Louisiana to Houston and picked 
up either three or four M15's from someones warehouse down near the ship 
channel.  As I recall, I paid something like the princely sum of $5 each to cover 
administrative costs.  That whole trip is a bit of a blur, punctuated briefly 
by almost getting run over by a GP-70 in Lake Charles.  :-)

It was only later after acquiring a bunch of other machines that I realized 
that the holding magnet selector was a rarety.  I think that was the only one I 
ever saw actually in a machine, although I've seen loose selectors since.  
And I have no idea what became of it.  I have no memory of still having it after 
I returned from Vietnam in late '68.  I might have given it to the LA Tech 
campus radio station before I left.  I did supply the two transmitters that they 
first went on the air with (a BC-610-F and a T-47/ART-13).

In a message dated 11/20/2007 11:08:54 PM Central Standard Time, 
drhouse at dls.net writes: 
> A an Illinois Bell Teletype Serviceman I personally did not see a  
> holding magnet version in service. Of course by 1966 we did not have  
> many 15s or 19s in service.  However, I am familiar with the use of 20  
> milliamp and 10 milliamp telegraph circuits.  These were usually set  
> up with the use of hubs for broadcast of weather information.  Many of  
> the loops were long and difficult to support 62.5 milliamps; so 20  
> milliamps was a second choice.  In the Chicago area there were many  
> weather machines... some shared the same loop in which case the two  
> machines each used a special selector assembly that operated on 10  
> milliamps.  I wonder if anyone on this list has any experience with 10  
> millamp machines?
> 
> I worked in the suburban area.  We did not have any machines set up to  
> run on either 20 or 10 milliamp loops.  All of our machines used 62.5  
> milliamps -130 vdc.  At least two of our machines (we had over 600 to  
> maintain) had long loops.  Rather than use 20 milliamp selectors we  
> used both the positive and negative supplies with two cable pairs tied  
> in parallel to reduce resistance.  NO ONE got near those pairs with  
> 260 volts 62.5 milliamps.  If you bumped that voltage it could put  
> your shoulder out of joint.  All places along the cable route had  
> special red rubber insulator caps warning of the high potential.   
> Later on the circuits were redesigned to run on -130 62.5 mA.
> 

Robert Downs - Houston
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