Page 19 - SAFAR

The single sprocket, mounted integrally with the flywheel , and cushioned by th e
spring couplings to the gear wheel, rotates very smoothly and evenly. It combines
the functions of feed and take-up sprockets and sound drum. The film is located on
both upper and lower surfaces of the sprocket by two cradles. These cradles do not
bear d irectly on the surface of the film within the image area; they are supported at
.a set gap of 0.0075 in. by means of flanges riding on the surface of the sprocket outside
the film area.

ELECTRICAL : The mains input is looped via two pins on the speaker plug, so
that removal of the speaker plug breaks the supply. The switch on the volume control
forms the main supply switch, but this shou. ld not be operated when motor and lamp
switches are on. The main transforme r supplies the following :
Primary I I 0 volts-Projection lamp ;
(Auto) 125 volts-Motor ( 160 v. some models)
(IIOv. , , )
Secondaries 4 volts-Rectifier heater.
6.3 volts-Valve heaters and pilot lamp. •
5.0 vo lts-Exciter lamp (unde r run ).
340 volts-(Biphase) H.T. rectifie r.
.
The motor su pply, via th e "Project " switch , also goes t hrough a heavy-d ut y
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resistor. In parallel with t his resistor, an arrange ment accomplished by means of slip .;
rings and brush es, is a co ntactor mou nt ed on a disc driven by the motor. The con-
tactor is arranged t o open und er the influence of ce ntrifugal force at a speed w hich
can be predetermined by t he st atic gap of t he contact o r. Thus at slow speeds th e
contacto r is closed , short-circuiting the resisto r so that the max imum volt age is ap plied
to the moto r. This resu lts in an increase in speed ; t he increase in cent rifugal fo rce
opens the co ntactor so that t he sho rt -circuit is re moved. Thus the vo ltage applied
to t he motor is red uced an d it slows. Then t he w hole cycle is re peated. In practice
t he contact or oscillates at t he crit ical parting speed, and t he speed of the motor is
held to close iimi ts. The movement of the contactor in o pe ning is transferred by a
lever to a stud, which bears against a screw con t ro l fo r mi ng t he speed co ntrol of th e
motor. Screwing in this st ud rest ri cts the move me nt of one of the contact ors so
t hat th ey open at quite a low moto r speed , w hilst wh e n th e st ud is fully out th e
contacto rs are al most permanent ly closed. T he st ud , therefore gi ves a usefu l moto r
speed range, w ith t he speed of rotati o n held to close lim its at any selected point
it hin t hat range. A conde nse r is co nn ect ed in pa rallel with the resist o r (and there-
ore w it h the cont actor) to red uce arcing on the governo r brushes and co ntactor .

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