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From: lagasse@biomed.UUCP (Robert C. Lagasse)
Newsgroups: net.ham-radio
Subject: Telephone Innards
Message-ID: <58@biomed.UUCP>
Date: Fri, 17-May-85 09:23:23 EDT
Article-I.D.: biomed.58
Posted: Fri May 17 09:23:23 1985
Date-Received: Sat, 18-May-85 02:10:16 EDT
Organization: Mass. Gen. Hosp. - Dept. Biomed. Engineering
Lines: 35


  I'm sure everyone who reads this group has opened up a telephone to see
what's going on inside.  No, I'm not writing about the new high-tech
single-piece electonic pulse phones, I mean the good old all-American
Western Electric black rotary dial desk phone.  The kind that hard-wired to
a wall junction block (called a 42A) with three or four wires (third was
ground and fourth was lamp supply for lighted sets which used an accessory
transformer hiding somewhere in your cellar).  I believe it is called a
"model 500" set or something.  The guts of this phone are still used in
5-line with hold systems and also with DTMF dialing desk sets from W-E.
  The large coil block riveted in the base which I believe is called the
"network" has about fifty screw terminals and has got to be one of the most
confusing pieces ever invented.  In the first place, this thing is labelled
with numbers and letters most of which are meaningless unless you are an
installer.  Half of the terminals are jumpered to others underneath where
you can't see and the others connect to coil windings and .......caps?? 
Anyway, this network thing is filled with thick sticky goop either to keep
people like myself out of it or to seal it from moisture.
  The other strangeness in this phone is the number of contacts used in the
"hook switch".  This switch must be a million-pole double-throw.  It seems
that the only things that would be needed to be switched are the network
(completely out of circuit) and the bell with it's series cap (in circuit)
when the phone is "on-hook" and vice-versa for "off-hook".  Sounds as if a
SPDT switch would do just fine or maybe a DPDT if you need contacts for a
dial lamp.
  Now that all of the phone stuff is deregulated, none of this must be
top-secret anymore.  Does anyone know where I can get the training manuals
that they teach the installers from?  Those guys amaze me when they open up
these phones and actually figure out how do anything they want to with them.
Also, where do all of these new modular jack numbers come from (RJ-11,
RJ-35, etc.) ?  Is there a committee somewhere dreaming these up and do they
relate to ANYTHING?    Comments appreciated.


Bob Lagasse  biomed. eng. MGH