Circuit Theory

A timer (1C2) is connected as a stable, free-running multivibrator whose frequency is externally con­trolled by pot R9 (see Figure 27-2). Resistor RIO selects the range limit of R9. Сapacitor C5, along with the resistors, determines the frequency range of the device. The square wave output of 1C2 is via pin 3 and is resistively coupled to power amplifier Q2.The drain of Q2 is DC biased through resonator choke LI.

The square wave output signal is now fed into transducer TD1 in a series with resonating coils L2 and L3 in a parallel com bination. The resonant action among the inherent capacities of TD1, the tuning capacitor C7, and the inductance now produces a sinusoidal-shaped wave peaking around 25 kHz or the upper limit of the tuning range. This signal wave­form now has a peak-to-peak voltage several times that of the original square wave. Transducer TD1 nov can take advantage of these peak voltages to produce the high-pressure-level sounds necessary without exceeding the high average ratings of an equivalent voltage-level square wave

Timer Id is similarly connected as a stable run­ning multivibrator and is used to produce the sweep­ing voltage necessary for modulating the frequency of

Figure 27-2 Phaser pain field gun schematic

Circuit Theory

Figure 27-3 PCB wiring

lC2.This sweep repetition rate is controlled by pot R2, and resistor R3 limits the range of this repetition time. Resistor R1 selects the duty cycle of the pulse, whereas capacitor C2 sets the sweep time range. The output for II is via pins 6 and 2 where the signal ramp function voltage is resistively coupled to inverter tran­sistor Ql via resistor R4. The output of Ql is fed to pin 5 of 12 and provides the output modulation volt­age necessary to vary the frequency as required. Note that the modulation signal is easily disabled via R2/S2.

Power to the system comes from battery B1 and pushbutton SI. Capacitor C6 guarantees an AC return path for the output signal. Power to the driver circuits IC1 and 1C2 come through a decoupling net­work consisting of resistor R7 and capacitor C3.

Construction Steps

To begin the assembly of the gun, follow these steps:

1. Lay out and identify all the parts and pieces, checking them with the parts list.

2. Cut the HS1 heatsink bracket from a.75 X 2 X.065 aluminum piece. Bend it 90 degrees at its midsection and drill a hole for the SW1/NU1 screw and nut. Then attach it to Q2 as shown later in Figure 27-4.

3. Figure 27-3 shows the assembly using a printed circuit board (PCB) available through www. amazingl .com. Experienced builders may use a piece of Л-inch grid perforated vec­tor board. Use the drawing for parts location and the schematic for the connections. Certain leads of the actual components will be used for connecting points and circuit runs. Do not cut or trim them at this time. It is best to tem­porarily fold the leads over to secure the indi­vidual parts from falling out of the board holes. If you obtain a PCB, you may omit this step.

4. Insert and then solder in the designated com­ponents:

a. Insert the ’/4-watt resistors: R1, R3, R4, R6, R7, R8, and R12.

b. Insert RIO and R13.

c. Solder in the control pots R2/S2 and R9. Use short pieces of bare-wire leads from the component pins to the respective holes in the PCB. Note these controls must be as close to the board surface as possible.

Note that Rll and R14 are not used and the positions for R15 and R16 are used for components designated as L2 and L3.

d. Insert capacitors Cl, C4, C5, and C8.

e. Insert electrolytic capacitors C2, C3, and C6, noting the polarity. Note that C7 is not used in this circuit.

f. Insert semiconductors Ql, Q2, IC1, and IC2. Note that Q2 is attached to heatsink HS1 via SW1/NU1.

g. Insert two wire jumps.

h. Insert the two 1 millihenry inductors in place of R15 and R16.

i. Insert the red lead of CLl and the 10-inch lead for SI as shown.

j. Insert two 10-inch leads for transducer TD1.

Circuit Theory

Figure 27-4 Assembly of inductor LI and heatsink HSI

5. Assemble the LI choke coil by wrapping 50 turns of #24 magnet wire on the nylon bobbin as evenly as possible. Leave two inches of leads for connection to the circuitry. Assemble the E core, as shown in Figure 27-4. Shim each side with pieces of yellow cardboard strips of

.003 inches each for a total of.006 inches. If you have an inductance capacitance bridge, measure 1.5 millihenry s.

6. Wire in the inductor and secure it to the board with room temperature vulcanizing (RTV) silicon rubber or another suitable adhesive.

7. Preconnect all the leads toTDl, Si, and CLl.

8. Check the complete wiring for potential shorts, wire bridge shorts, poor solder joints, the correctness of the components, and the position and orientation of Ql, Q2, C3, C6, ICl, and IC2.

Leave a Reply

Your email address will not be published. Required fields are marked *

Confirm that you are not a bot - select a man with raised hand: