Learn about computer

The action of this receiver will be understood when it is stated that
in common-battery practice, as will be shown in later chapters, a
steady current flows over the line for energizing the transmitter. On
this current is superposed the incoming voice currents from a distant
station. The steady current flowing in the line will, in the case of
this receiver, pass through the magnet winding and establish a normal
magnetic field in the same way as if a permanent magnet were employed.
The superposed incoming voice currents will then be able to vary this
magnetic field in exactly the same way as in the ordinary receiver.
An astonishing feature of this recent development of the so-called
direct-current receiver is that it did not come into use until after
about twenty years of common-battery practice. There is nothing new in
the principles involved, as all of them were already understood and
some of them were employed by Bell in his original telephone; in fact,
the idea had been advanced time and again, and thrown aside as not
being worth consideration. This is an illustration of a frequent
occurrence in the development of almost any rapidly growing art. Ideas
that are discarded as worthless in the early stages of the art are
finally picked up and made use of. The reason for this is that in some
cases the ideas come in advance of the art, or they are proposed
before the art is ready to use them. In other cases the idea as
originally proposed lacked some small but essential detail, or, as is
more often the case, the experimenter in the early days did not have
sufficient skill or knowledge to make it fit the requirements as he
saw them.
Monarch Receiver. The receiver of the Automatic Electric Company
just discussed employs but a single electromagnet by which the initial
magnetization of the cores and also the variable magnetization
necessary for speech reproduction is secured. The problem of the
direct-current receiver has been attacked in another way by Ernest E.
Yaxley, of the Monarch Telephone Manufacturing Company, with the
result shown in Fig. 54. The construction in this case is not unlike
that of an ordinary permanent-magnet receiver, except that in the
place of the permanent magnets two soft iron cores _1-1_ are employed.
On these are wound two long bobbins of insulated wire so that the
direct current flowing over the telephone line will pass through these
and magnetize the cores to the same degree and for the same purpose as
in the case of permanent magnets. These soft iron magnet cores _1-1_
continue to a point near the coil chamber, where they join the two
soft iron pole pieces _2-2_, upon which the ordinary voice-current
coils are wound. The two long coils _4-4_, which may be termed the
direct-current coils, are of somewhat lower resistance than the two
voice-current coils _3-3_. They are, however, by virtue of their
greater number of turns and the greater amount of iron that is
included in their cores, of much higher impedance than the
voice-current coils _3-3_. These two sets of coils _4-4_ and _3-3_ are
connected in multiple. As a result of their lower ohmic resistance the
coils _4-4_ will take a greater amount of the steady current which
comes over the line, and therefore the greater proportion of the
steady current will be employed in magnetizing the bar magnets. On
account of their higher impedance to alternating currents, however,
nearly all of the voice currents which are superposed on the steady
currents, flowing in the line will pass through the voice-current
coils _3-3_, and, being near the diaphragm, these currents will so
vary the steady magnetism in the cores _2-2_ as to produce the
necessary vibration of the diaphragm.
[Illustration: Fig. 54. Monarch Direct-Current Receiver]
This receiver, like the one of the Automatic Electric Company, does
not rely on the shell in any respect to maintain the permanency of
relation between the pole pieces and the diaphragm. The cup _5_, which
is of pressed brass, contains the voice-current coils and also acts as
a seat for the diaphragm. The entire working parts of this receiver
may be removed by merely unscrewing the ear piece from the hard rubber
shell, thus permitting the whole works to be withdrawn in an obvious
manner.

Before considering the various types it is well to state that the term
telephone is often rather loosely used. We sometimes hear the receiver
proper called a telephone or a hand telephone. Since this was the
original speaking telephone, there is some reason for so calling the
receiver. The modern custom more often applies the term telephone to
the complete organization of talking and signaling apparatus, together
with the associated wiring and cabinet or standard on which it is
mounted. The name telephone set is perhaps to be preferred to the word
telephone, since it tends to avoid misunderstanding as to exactly what
is meant. Frequently, also, the telephone or telephone set is referred
to as a subscribers station equipment, indicating the equipment that
is to be found at a subscribers station. This, as applying to a
telephone alone, is not proper, since the subscribers station
equipment includes more than a telephone. It includes the local wiring
within the premises of the subscriber and also the lightning arrester
and other protective devices, if such exist.
To avoid confusion, therefore, the collection of talking and signaling
apparatus with its wiring and containing cabinet or standard will be
referred to in this work as a telephone or telephone set. The receiver
will, as a rule, be designated as such, rather than as a telephone.
The term subscribers station equipment will refer to the complete
equipment at a subscribers station, and will include the telephone
set, the interior wiring, and the protective devices, together with
any other apparatus that may be associated with the telephone line and
be located within the subscribers premises.
Classification of Sets. Telephones may be classified under two
general headings, magneto telephones and common-battery telephones,
according to the character of the systems in which they are adapted to
work.
_Magneto Telephone._ The term magneto telephone, as it was originally
employed in telephony, referred to the type of instrument now known as
a receiver, particularly when this was used also as a transmitter. As
the use of this instrument as a transmitter has practically ceased,
the term magneto telephone has lost its significance as applying to
the receiver, and, since many telephones are equipped with magneto
generators for calling purposes, the term magneto telephone has, by
common consent, come to be used to designate any telephone including,
as a part of its equipment, a magneto generator. Magneto telephones
usually, also, include local batteries for furnishing the transmitter
with current, and this has led to these telephones being frequently
called local battery telephones. However, a local battery telephone is
not necessarily a magneto telephone and _vice versâ_, since sometimes
magneto telephones have no local batteries and sometimes local battery
telephones have no magnetos. Nearly all of the telephones which are
equipped with magneto generators are, however, also equipped with
local batteries for talking purposes, and, therefore, the terms
magneto telephone and local battery telephone usually refer to the
same thing.
_Common-Battery Telephone._ Common-battery telephones, on the other
hand, are those which have no local battery and no magneto generator,
all the current for both talking and signaling being furnished from a
common source of current at the central office.
_Wall and Desk Telephones._ Again we may classify telephones or
telephone sets in accordance with the manner in which their various
parts are associated with each other for use, regardless of what parts
are contained in the set. We may refer to all sets adapted to be
mounted on a wall or partition as _wall telephones_, and to all in
which the receiver, transmitter, and hook are provided with a standard
of their own to enable them to rest on any flat surface, such as a
desk or table, as _desk telephones_. These latter are also referred to
as portable telephones and as portable desk telephones.
In general, magneto or local battery telephones differ from
common-battery telephones in their component parts, the difference
residing principally in the fact that the magneto telephone always has
a magneto generator and usually a local battery, while the
common-battery telephone has no local source of current whatever. On
the other hand, the differences between wall telephones and desk
telephones are principally structural, and obviously either of these
types of telephones may be for common-battery or magneto work. The
same component parts go to make up a desk telephone as a wall
telephone, provided the two instruments are adapted for the same class
of service, but the difference between the two lies in the structural
features by which these same parts are associated with each other and
protected from exposure.
[Illustration: Fig. 142. Magneto Wall Set]
[Illustration: Fig. 143. Magneto Wall Set]
Magneto-Telephone Sets. _Wall._ In Fig. 142 is shown a familiar type
of wall set. The containing box includes within it all of the working
parts of the apparatus except that which is necessarily left outside
in order to be within the reach of the user. Fig. 143 shows the same
set with the door open. This gives a good idea of the ordinary
arrangement of the apparatus within. It is seen that the polarized
bell or ringer has its working parts mounted on the inside of the door
or cover of the box, the tapper projecting through so as to play
between the gongs on the outside. Likewise the transmitter arm, which
supports the transmitter and allows its adjustment up and down to
accommodate itself to the height of the user, is mounted on the front
of the door, and the conductors leading to it may be seen fastened to
the rear of the door in Fig. 143.

The construction of the “in-tune” harmonic ringer employed by the Dean
Electric Company, of Elyria, Ohio, is illustrated in Figs. 180, 181,
and 182. It will be seen from Fig. 180 that the general arrangement of
the magnet and armature is the same as that of the ordinary polarized
ringer; the essential difference is that the armature is
spring-mounted instead of pivoted. The armature and the tapper rod
normally stand in the normal central position with reference to the
pole pieces of the magnet and the gongs. Fig. 181 shows the complete
vibrating parts of four ringers, adapted, respectively, to the four
different frequencies of the system. The assembled armature, tapper
rod, and tapper are all riveted together and are non-adjustable. All
of the adjustment that is done upon them is done in the factory and
is accomplished, first, by choosing the proper size of weight, and
second, by forcing this weight into the proper position on the tapper
rod to give exactly the rate of vibration that is desired.
[Illustration: Fig. 182. Dean In-Tune Ringer]
An interesting feature of this Dean harmonic ringer is the gong
adjustment. As will be seen, the gongs are mounted on posts which are
carried on levers pivoted to the ringer frame. These levers have at
their outer end a curved rack provided with gear teeth adapted to
engage a worm or screw thread mounted on the ringer frame. Obviously,
by turning this worm screw in one direction or the other, the gongs
are moved slightly toward or from the armature or tapper. This affords
a very delicate means of adjusting the gongs, and at the same time one
which has no tendency to work loose or to get out of adjustment.
[Illustration: Fig. 183. Kellogg In-Tune Ringer]
In Fig. 183 is shown a drawing of the “in-tune” harmonic ringer
manufactured by the Kellogg Switchboard and Supply Company. This
differs in no essential respect from that of the Dean Company, except
in the gong adjustment, this latter being affected by a screw passing
through a nut in the gong post, as clearly indicated.
In both the Kellogg and the Dean in-tune ringers, on account of the
comparative stiffness of the armature springs and on account of the
normal position of the armature with maximum air gaps and consequent
minimum magnetic pull, the armature will practically not be affected
unless the energizing current is accurately attuned to its own natural
rate. When the proper current is thrown on to the line, the ball will
be thrown into violent vibration, and the ends of the armature brought
into actual contact with the pole pieces, which are of bare iron and
shielded in no way. The armature in this position is very strongly
attracted and comes to a sudden stop on the pole pieces. The gongs are
so adjusted that the tapper ball will have to spring about one
thirty-second of an inch in order to hit them. The armature is held
against the pole piece while the tapper ball is engaged in striking
the gong and in partially returning therefrom, and so strong is the
pull of the pole piece on the armature in this position that the
accelerating influence of the gong has no effect in accelerating the
rate of vibration of the reed.
[Illustration: Fig. 184. Circuits of Dean Harmonic System]
_Circuits_. In Fig. 184 are shown in simplified form the circuits of a
four-station harmonic party line. It is seen that at the central
office there are four ringing keys adapted, respectively, to impress
on the line ringing currents of four different frequencies. At the
four stations on the line, lettered A, B, C, and D, there are four
harmonic bells tuned accordingly. At Station A there is shown the
talking apparatus employing the Wheatstone bridge arrangement. The
talking apparatus at all of the other stations is exactly the same,
but is omitted for the sake of simplicity. A condenser is placed in
series with each of the bells in order that there may be no
direct-current path from one side of the line to the other when all of
the receivers are on their hooks at the several stations.

Very well made CGI footage of the Hiroshima nuclear bomb blowing up.

read more | digg story

David Letterman explains why he doesn’t have a computer, and no intention to get one.

read more | digg story

Once upon a time, the four to eight gigabyte footprint of a DVD on your hard drive was prohibitively large. But since the price of a gigabyte has plummeted, ripping your entire DVD collection to your computer is not just possible, it’s prudent, and it’s easy. Let’s take a look at the best ways to back up and play any DVD rip on your home computer

read more | digg story

Clean your computer screen through the internets!

read more | digg story

Picotux…worlds smallest computer

read more | digg story

One of my favorite SNL sketches.

read more | digg story

A classic Simpson’s clip. "Look at the American Computer Monkey!!!"

read more | digg story