Click to enlarge
Picture: JM CHERRY
DESCRIPTION.
The RY-4 RTTY adapter allows the 50 kHz BFO in the SPR-4 to be remotely switched so that standard RTTY tones may be centered in the pass-band of the 50 kHz IF filter. The switching is accomplished by an external circuit which shorts the RTTY jack to ground. With the MODE switch in the CW position and the RTTY jack grounded, the BFO frequency will be switched to 48.590 kHz so that standard 2125 and 2295 Hz tones may be received. When the MODE switch is in the LSB position and the RTTY jack is shorted, the BFO will be switched to 49.350 kHz so that standard 2125 and 2975 Hz tones may be received. When the MODE switch is in the AM or USB position, shorting the RTTY jack will have no effect.
INSTALLATION.
 Click to enlarge Figure 1 |
 Click to enlarge Figure 2 |
 Click to enlarge Figure 2 |
 Schematic |
| Picture: R.L. DRAKE Company | |
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Disconnect the speaker cable and the line cord. |
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Remove the 12 black screws from the sides of the cabinet. Mount the circuit board to the location shown in figure 1 using a No. 4 sheet metal screw with a No. 4 lockwasher between the screw head and the mounting foot. Some early SPR-4 Receivers may not have the hole in the chassis. In this case, mount the circuit board foot under the No. 6 nut on the PTO spade bolt as shown in figure 1. |
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Mount the phono jack (with nut, lockwasher and ground lug on the inside of the chassis) in the hole next to the grounding screw on the rear apron of the chassis. Connect the .01 mF capacitor between the phono jack and ground lug. Solder only the ground lug. Connect the 3 wires between the terminals on the RY-4 circuit board and the terminals on the BFO board as shown in figure 2. |
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Use bare wire and sieving. DO NOT use any more heat than necessary when soldering the terminals as the circuit boards may be damaged. |
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Connect the 3 color coded wires between the RY-4 circuit board terminals and switch S-14R as shown in figure 2. |
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Connect a wire between the RY-4 circuit board terminal and the phono fitting. Dress the wire along the wiring harness. Solder all connections. |
ALIGNMENT.
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The BFO transformer, T-17, must be adjusted for 50 kHz. Place the MODE switch in the USB position and the RF GAIN control fully clockwise. The position of the CRYSTAL SELECTOR, the RANGE switch, and the PRESELECTOR is unimportant. |
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Connect a clip lead with a series blocking capacitor larger than 1,000 pF between the terminal on T-15 and the 10 K resistor of the SCC-4 Crystal Calibrator. See figure 1 and figure 3. |
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Adjust the slug in T-17 for zero beat. |
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Remove the clip lead and replace the cabinet. |
