The Electrical experimenter

40 THE ELECTRICAL EXPERIMENTER May, 1917
THE
A Simple Electric Motor Attachment
for Phonographs
phonograph is without doubt one
of the greatest of all pleasure giving
instruments. This fact is amply
demonstrated by the large numljer of these
machines in
is, however,
use
like
at tlie present time.
many other articles,
It
appreciated
most wlien new, and is little used
By R. U. CLARK, 3rd
at a constant speed by the governor with
which the talking machine is fitted, may
appear rather inappropriate, but. altho
some heating does take place in this motor
it is not sufficient to cause e.xcessive wear
or shorten its life materially.
The actual method of driving the talk-
Illustrating How the Author Devised a Simple and Effective Electric Motor Drive for a
Disc Style Talking Machine. The Old Governor Mechanism Is Retained and the Motor Drives
the Record Table by Means of a String or Cord Belt. (Fig. 1.)
after its novelty wears ofT, owing to the
constant attention required to operate it.
Winding up the spring to keep the motor
going is the one thing which detracts most
from the pleasure which should be derived
from any good talking machine.
By means of a simple electric motor attachment
it is at once possible to do away
with practically all the bother incident to
the operation of the talking machine, with
the exception of changing the records.
Most of the standard machines on the
market today lend themselves very readily
to the attachment of an auxiliary motor
device, so that, by the employment of a
little care and ingenuity, it is a simple
matter to remodel a phonograph so as to
run it by electric motive power.
The actual amount of power required
to drive the turntable of most any phonograph
at the proper speed is very small,
although it may not appear so to the person
who has to be continually winding up
the ordinary spring motor. Just how little
power will suffice depends more or less on
the machine to be driven, but for most
machines a universal electric motor of 1/40
H.P. will be found quite sufficient. These
motors can be purchased new in most cases
for as little as $4 complete, and can be
attached by a flexible wire direct to the
ordinary lamp socket, without using any
extra resistance. The motor used by the
author with considerable success was
bought originally as a fan motor for $4;
the fan, guard, and base which came with
the motor were removed.
The motor mentioned above was designed
to drive a six-inch fan at about
3,000 r.p.m. Under this load the makers
claim it can be run at a cost of about 1
cent per 6 hours, the rate per K.W. being
10 cents. This motor is equipped with
special patented bearings which require no
oiling; for about 2 months, during which
time the author's machine has been run a
great deal, no oil has been placed on the
bearings.
The use of such a small motor, as mentioned
above, for such exacting work as
running a large turntable, which is held
ing machine turntable on which the records
rest, as described in this article, is by direct
belt connection, which method requires
perhaps the least accuracy in construction.
The author after considerable experimenting
with a simple friction drive, direct
from the electric motor shaft, which was
fitted up with various rubber and composition
friction wheels, was forced to
give up this method in the favor of belt
drive. Friction drive applied to such a
mechanism as the phonograph requires
very accurate construction, and even then
direct friction drive on most machines
would prove noisy and imsatisfactory, due
motor, but does not effect the speed governing
mechanism, which is left in place,
for use with the electric inotor, to control
the speed in the usual manner.
.-\fter disconnecting the spring motor
from the turntable shaft, the table should
be removed and a small groove from 1/32
to 1/16 of an inch deep, the actual depth
depending
table rim,
on the thickness of the turn-
should be made for the belt to
run in around the outside of the rim. This
groove should be about Jg of an inch wide,
and should
of the rim.
not be too near the top edge
On certain machines there is
a narrow shoulder located under the rim.
which in
As the
some cases will hold the belt.
phonograph is to be driven by a
belt a small grooved pulley wheel for the
motor is necessary. This wheel is best
made of metal with a small groove about
Yi inch wide, either V or semi-circular in
cross-section, and about 1/16 inch deep.
The greatest diameter of the pulley should
be about 1 inch or under. The author
has used e.\perimentally several sizes from
5,^ inch up to 1 inch, all with considerable
success, but when a 1 inch wheel is used,
the motor which then turns at about 800
r.p.m. seems to run the quietest, and with
practically no belt slippage. Within the
sizes mentioned the diameter of the pulley
will have little effect upon the speed of
the turntable, which
its own governor as
is still controlled by
mentioned above, but
of course the motor pulley-belt speed will
be decreased by the use of a small pulley
and increased when a large pulley is employed.
.\ 10 cent pulley from a mechanical
toy set is satisfactory.
The metl.od to be used in mounting the
motor will necessarily depend somewhat
upon the type of talking machine used.
There are two simple ways of attaching
the motor, one of which should be applicable
to nearly any machine made. Wherever
the construction of the talking machine
permits, the motor can be hung out
of sight, from the top-board of the body
of the phonograph, with the shaft extending
so that
thru this
the pulley
board
wheel
about
can be
16 inch.
mounted
with ease from the top side of the board
on which the motor is hung, as shown in
Fig. 1. This mode of mounting is possible
to the notoriously imperfect, peripheral only with a certain class of phonographs,
arc described by most talking machine mostly the larger sizes. For use with
turntables.
small machines, where the motor cannot be
The first step in the preparation of the
talking machine for the addition of an
electric motor is to run the machine until
hung out of sight, it can be inverted and
fastened to the top board, in such a manner
that the pulley groove, which comes
the spring is completely imwound. This next in position to the motor bearing,
requires about fifteen minutes time. The with the hub near the outside end of the
spring motor and top board is then re- shaft, comes in line with the grooved pormoved
temporarily from the phonograph,
if possible, by removing the crank handle.
tion of the turntable. (See Fig 2.)
To use the method of attachment first
In some machines it
is possible to get at
the motor from the
bottom, .^s soon as
access to the motor
is obtained, the gears
and shaft, which
form the connecting
link between the
turntable shaft and
the spring motor
gears are removed.
The unit
moved is
to be
clearly
reindicated
in Fig. 1, .\
A. The heavy center
line A—.\ which
passes thru the lower
Where it is Not Possible to Conceal the Motor in the Cabinet, as
(n >Small Machines, the Motor Can Be Readily Mounted Above the
Cabinet Shelf as Shown. (Fig. 2.)
part of the spring
motor casing indicates the position of the
unit to be tr.ken out. Removing thi? piece,
by letting up on the set screws, which hold
the pivot bearings, on which the shaft
mentioned above runs, simply disconnects
the turntable and its shaft from the spring
described it is necessary to drill three holes
in the top board spaced about 2 inches
from the edge of the turntable. The
center hole is made to accommodate the
main bearing and shaft of the motor. The
(Continued on page 76)