From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Service information and adjustment procedures for a Superheterodyne radio receiver.
| Identifier | ExFiles\Box 63\3\ scan0105 | |
| Date | 4th November 1934 guessed | |
| SERVICE INFORMATION Circuit: Superheterodyne—Intermediate Frequency 172½ k.c. Tubes and their functions: 1—78 Radio frequency amplifier. 1—6A7 {Electron coupled oscillator. First detector. 1—78 Intermediate frequency amplifier. 1—75 {Diode second detector. Audio frequency amplifier. Automatic volume control. 1—41 Output power tube. 1—84 Full-wave rectifier. 1—Non-synchronous vibrator inverter. The function of the vibrator is to convert direct current from the battery into alternating current to actuate the power transformer. Voltage Analysis: Note: All “B” and “C” voltages should be measured on a high resistance voltmeter of 1000 ohms per volt or over. The voltages are measured to ground from the points named. Ground the antenna to its shield when taking readings. Battery volts—6. Volts across heaters—6 scant. Volts across speaker field—6 scant. Tube Plate Screen Cathode Suppressor Osc. plate 78 110 110 6 6 6A7 170 110 6 170 75 110 1.3 78 110 3.5 3.5 41 210 220 15 If the set fails to operate look for some minor cause which might be one of the following:— 1. No “A” supply—“A” lead to set not making contact with ammeter post. Fuse blown. 2. Low “A” supply—The car battery needs recharging. 3. Tubes not in place in their sockets. 4. Grid caps not in place. 5. Defective tubes. 6. Antenna lead shorted to shield at splice, or otherwise grounded. A 10-ampere fuse is located in a small tubular holder in the battery lead. To replace the fuse, remove the cap, insert the fuse and replace the cap. The fuse is intended to protect the receiver and in no case should one larger than 10 amperes be used. ADJUSTMENTS The receiver was carefully adjusted and tested by experts at the factory, and should reach the customer in perfect condition. Under no circumstances should these adjustments be disturbed unless it is absolutely necessary as in the repairing of a damaged set. This should be done by an experienced Auto Radio Service man only. Intermediate Transformers To align the intermediate frequency transformers, use a good modulated oscillator set for 172½ k.c. Set the volume control for maximum volume and turn the dial to a point where little or no signal is received; then ground the antenna. Connect the oscillator output between the grid of the 6A7 tube and ground. Connect an output meter across the primary of the speaker transformer or across the voice coil. Using the smallest output from the test oscillator that will give a small reading on the meter, adjust the two I.F. transformers for the largest reading obtainable. Use a non-metallic screw driver if possible. Radio Frequency and Oscillator To align the R.F. and oscillator sections, couple the oscillator through a standard dummy antenna to the antenna lead and ground of the receiver. Set the test oscillator to some frequency between 1350-1450 k.c. Set the dial to the frequency selected. Adjust trimmers on the variable condenser beginning with the oscillator trimmer. Reduce the output of the test oscillator and repeat. In the absence of an oscillator, the R.F. sections may be aligned on broadcast. Tune in a weak station between 1350 and 1450 k.c. and align as before. If an output meter is not available, adjust for maximum volume, then reduce the input and repeat. ADDITIONAL NOTES ON SUPPRESSION The measures to be adopted for the suppression of ignition interference as stated previously should be adequate for the majority of installations. There are however, stubborn cases which may not respond so readily to the ordinary methods. A great source of annoyance on some cars might be the wire leading to the dome light, the leads to the primary of the ignition coil and the lead from the secondary of this coil to the distributor, (especially when the coil and distributor are some distance apart). Other sources of interference are poor contact of distributor and spark-plug leads with the distributor contacts,—wide spacing between distributor contacts,—breaker points too far apart,—pitted breaker points. The remedies for the above suggest themselves, but will be given here briefly. By-pass ammeter with a ½ mfd condenser close to it. By-pass dome light wire at the instrument panel with a ½ mfd condenser. By-pass the low tension lead to the ignition coil with a ½ mfd condenser. Shield the wiring to the ignition coil; ground the shield to motor frame. Shield the high tension lead from the coil to the distributor, grounding the shield to the motor frame and fire wall. | ||