[GreenKeys] ST6 questions

[Don Robert House]

At one time almost all telephone cables over 12,000 feet had all of  
their cable pairs "loaded" with 88mH coils which came in large "cans"  
with a splicing stub.  The 88mH toroids were placed every 6,000  feet  
to cancel the capacitance of a section of cable.  This made the cable  
"flat" in frequency response within the voice band of 300-3200 Hz.  
Most of these cables were either 22 awg or 24 awg.  Urban telegraph  
design cable was usually 19 awg and not loaded.  You can imagine the  
cost of copper and lead for these cables and toroids.  Some rural  
cables were 16 awg aluminum and used a different loading scheme.   
When and end section was an odd length we had to install "build-out"  
capacitors on all the pairs.  When digital transmission started about  
1974 many many cables had to have their "loaders" and "bridged taps"  
removed.  Starting in 1975 the cost of toroids should have started to  
come down as they became available (and still are) on the surplus  
market.

Don,  Ye Old Telephone Man --- "Transmission Engineers do it 'til it  
Hertz"


On 17 Jul 2006, at 2:06 PM, Bill Henry wrote:

Don and all --

Thanks for the comments.

Not so much a "do good doer" - but that I am old enough to remember  
and want to write it down before I forget.

Toroids were a fun thing and the absolute best bargain in electronics  
at the time.  Those are very high quality coils.  At the peak of the  
ST-6 work, we paid between $0.05 and $.25 each, depending on the  
source.  And then we'd have to strip them out of the casings,  
separate the coils, and strip and tin the leads.  We easily put  
another two or three bucks into every one.  When the surplus market  
started to dry up, I tried to have some new ones made.  Automatic  
Electric in Chicago wanted a minimum  order of 10,000 and the price  
was $7.50 - EACH - and that was in 1972 dollars!  For a little bitty  
garage company, it might as well been a million bucks.  Plus, each  
ST-6 plus AK-1 had 10 toroids and the parts kit sold for $100 or so.   
This would have just about doubled the price!  As they say, the rest  
is history - ST-6000 and then ST-5000.

Bill