A technical discussion

[joey67]

I would like to have a technical component level explanation of how my 1955 Western Electric model 500 phone works.  I am currently an electronics student about half way through earning my associates degree.  This is the technical level that I would like to have this discussion on, please.
For example, what is the component level circuit path of the dial tone when the phone is off hook?
What is the component level circuit path of the ringing?
I would like to know all aspects on a component level how this phone works. If anyone can indulge me with these explanations please, thanks in advance for your time. 

[Phonesrfun]

Hi Joey:

Your best bet, without spending $25.00 on a book is to go to www.oldphoneguy.net ( dead link 03-18-22 )
  (Colin Chamber's website) and download the Army telephone manual in pdf and study it.  (Choose the topic "Big Books" from the index in the left margin of the web page)

That information is in the 1955 timeframe on a phone that does not use supplementary circuitry for sidetone and loop compensation, which only serve to complicate the discussion.

The base circuit described in that army manual is exactly the base circuit used in all analog phones, that were made right up until the '90's and some even today.

You will find that the transmitter is in series with the primary of an induction coil, and that the receiver is in the secondary winding of the induction coil, which isolates the receiver from the DC path of the phone line.  The battery is provided by the central office.  Everything else revolves around this concept.

In reading, you will also need to understand how that battery is provided on the phone line and how it is that a single battery can provide talk battery to thousands of phones without everyone being able to hear everyone else.  The manual on Colin's website covers it all.

Happy reading.

[dsk]

Hi
The hints above are good.
   
"Consumer electronics for engineers"  of  Hoff, Philip Herbert has a page explaining some of it. The Army manual: TM11-5865-256-13 describing the field telephone TA-43PT does it more accurate, but still not exact. The Ta-43PT;  The principle of the circuit  is equal to the 500, but the primary winding is splitted into two half's on the 500, and the receiver and receiver winding of the coil has changed place in the serial circuit.

Good luck

dsk

[Phonesrfun]

It is probably up to Joey where to start, but the more basic circuit in the Army manual explains it pretty well.  When you get into the refinements of the double primary and tertiary windings that are there only to enhance sidetone reduction, provide for vcurrent equalization and provide other features for automatic number identification, I personally have a tendancy to get bogged down in the vector analysis that ultimately comes out of the discussions.

Besides, even the basic 302 still works great on phone lines, and is what the 500 circuit has at its root.