Operation Of Model 215 Impulse Transmitter; Operation Of Model 216 Impulse Receiver - Wurlitzer 3020 Service Instructions And Parts Catalog

Service Instructions
Section
I
CYCLE OF SELECTION
After a coin has been inserted and registered, the
wallbox is ready for a selection. When any one of the
24 selector buttons is depressed , the following cycle
takes place:
The coin relay remains open, keeping the selector
circuit closed through its normally closed contacts 5
and 6. (See Figures 4, 5, and 6. ) The motor is started
by the 117 volt contacts on any one of the selector but·
ton switches which are in series with contacts 3 and 4
of the selector button relay and in parallel with the
full cycle switch. The selector buttons are latched
mechanically through cam action, powered by the rno·
tor. The selector contact arm rotates to complete the
cathode circuit of the transmitter through contacts I
and G. This generates . a long R.F. pulse or signal
which is transmitted over. the 117 volt power lines to
the phonograph. This pulse, or signal, comes out of
the junction box through terminals 32 and 33, of the
. B connector stepper socket, into the stepper and out •
through the 12 prong socket terminals 6 and 12 to
the receiver 12 prong plug terminals 6 and
1~,
which
are the receiver R.F. Input terminals. The signal is
~hen
amplified and passes through the receiver, there·
by actuat ing the receiver relay. The contacts of the re·
ceiver relay complete the circuit to terminals 5 and
8 of the 12 prong receiver plug and through terminals
5 and 8 of the 12 prong stepper socket, the circuit
is completed to energize . the stepper coil. This first
long R.F. pulse closes the stepper coil thereby advanc-
ing the stepper contact arm one step. It also corn·
pletes the circuit through its contacts l and 2
~o
the
coil of the timing relay which closes. The clos1ng of
the timing relay and its
conta~ts
l and 2 completes a
circuit to close the release latch relay. Additional
R.F. pulses picked up by the receiver advance the
stepper contact arm to the desired point o( selection.
As the motor completes its cycle, cam action cancels
one registration on the ratchet wheel and also releases
the selector button latch bar permitting the selected
button to return to a normal position through spring
loading.
OPERATION OF MODEL 215
IMPULSE TRANSMinER
The Model 215 Impulse Transmitter consists of a
6V6GT /G oscillator rube, a 6XSGT /G rectifier tube
and other associated components. (See Figure 4.) The
oscillator frequency is controlled by a quartz crystal
in the 6V6GT/G grid circuit. The 6Y6GT/G plate
circuit is runed to the crystal frequency at the factory.
This tuning, generally, should not be molested in the
field. The oscillator is keyed in the cathode circuit
by means of the rotating contact arm as it rides over
the contact scrips.
The secondary or output coil, coupled to the oscil-
lator coil connects to the A.C. line when a selection
General Description
is being made, through the .1 MFD C-8 condenser and
the frequency change switch. The C-8 condenser pre-
vents 60 cycle current from affecting the output coil
but does not impede the radio frequency signal being
transrni tted.
Transmitters are shipped from the factory equipped
with a red crystal unit and with che three-posicion
switch turned to "RED". Blue and yellow crystals are
available from the Service Department, but should be
used only when it becomes necessary to change fre-
quency on one of two locations close together to avoid
interference. The three crystal units (red, blue and
yellow ) provide three operating frequencies . When
blue or yellow crystals are used, the transmitter switch
must be turned
to
the corresponding color position.
The transmitters are carefully peaked or tuned,
working into a proper load at the factory. In general,
it is advisable not to attempt to improve on the fac-
tory adjustment on location, because it is possible to
upset the peaking enough co prevent the crystal from
oscillating during normal wallbox keying. Repeaking
of the transmitter can best be done in the Distributor's
or Operator's Service Department, which is
~quipped
with suitable test apparatus.
OPERATION OF MODEL 216
IMPULSE RECEIVER
The Model 216 Impulse Receiver installed in the
phonograph, gets its filament and " B" power from the
stepper into which its plugs. The tube complement
includes a 6SK7 amplifier, a 6SQ7 detector and D .C.
amplifier, a 5Y3GT rectifier and a 6SN7GT for oper-
ating the relay. An additional cube, a 6U5/6G5, is
used for tuning the receiver. This may be purchased
from your Distributor.
Signals from the wallboxes are amplified by the
6SK7 tube and are then rectified by the diodes 'of the
6SQ7 tube. (See Figure 6). Each diode of the 6SQ7
rube is connected to a separate secondary winding of
the second R.F. transformer. One diqde c- ircuit sup-
plies a lengthened pulse of negative potential for the
6SK7 grid, which makes the receiver less sensitive to
extraneous noise between pulses. The other diode cir-
cuit supplies a signal pulse, also of negative polarity.
co the 6SQ7· grid, causing the triode section to become
non-conducting. With no signal, the triode section
conducts, causing the 6SQ7 plate and 6SN7 grids to
become more negative than the 6SN7 cathode, so that
the 6SN7 draws no plate current.
The triode section of the 6SQ7 and the paralleled
sections of the 6SN7 form a direct coupled D.C. am-
plifier. With no signal coming in, the 6SQ7 triode
conducts and the 6SN7 is cut-off. When signals are
received, each pulse causes a negative voltage co ap-
pear on the 6SQ7 grid and drives it to cut-off, i.e., it
does not· draw plate current. The potential of the
6SQ7 plate and. 6SN7 grids immediately rises to chat
of the 6SN7 cathodes and the 6SN7 conducts, thereby
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