Airmec_211维修电路原理图.pdf

RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 2 OF 37 www.TheValvePage.Com RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 3 OF 37 www.TheValvePage.Com RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 4 OF 37 www.TheValvePage.Com RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 5 OF 37 www.TheValvePage.Com RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 6 OF 37 www.TheValvePage.Com RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 7 OF 37 www.TheValvePage.Com RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 8 OF 37 www.TheValvePage.Com INTRODUCTION The RadiVet has been designed and built primarily as a very compact piece of test gear for checking, aligning and locating faults in all stages of FM receivers. The facilities provided also enable tests to be carried out on Public Address equipment, tape decks, and AM broadcast receivers. Basically the RadiVet consists of three independent instruments housed in one case: an AM/FM signal generator, with crystal calibration, an audio oscillator and an oscilloscope. These three instruments, which can be used either separately or in conjunction one another, enable every function of a receiver to be thoroughly investigated. The interconnections required for the different tests are set up by means of switches on the front panel. A brief summary of the facilities of the RadiVet is given in Section 2 from which an experienced service engineer will be able to work out his own methods of employing the instrument. Full instructions for operating the RadiVet to obtain each of the facilities are given in Section 3, and the application of these facilities to testing FM and AM receivers, audio amplifiers, tape recorders and television receivers are dealt with in Sections 4 to 8. A detailed technical description of the circuit appears in Section 9, a specification in Section 10 and maintenance instructions in Section 11. 1. SUMMARY OF FACILITIES The facilities provided by the RadiVet are listed below and further information on voltage ranges, accuracy, etc. is given in Section 10. Signal Generator The signal generator covers the frequency ranges 0 to 15 mc/s and 85 to 100 mc/s, that is the normal broadcast AM band and FM IF band, and the FM transmission band. The output is in each case obtained by mixing the outputs of two oscillators, one of which may be frequency modulated and the other amplitude modulated. The signal may therefore be un-modulated, modulated with FM or AM or simultaneously with FM and AM at different modulating frequencies. In addition, signals in the bands 0-30 mc/s, 45-60 mc/s, 65-80 mc/s and 195-240 mc/s are obtainable at a lower output level (see Sect. 8). The signal generator output is fed through a coaxial cable, to a probe unit which contains an attenuator. Output signal levels between approximately 5 micro-volts and 50 milli-volts may be obtained. 1.1. Wobbulator The signal generator may be frequency modulated at 50 c/s with a frequency sweep of up to 500 kc/s. If this signal is applied to the IF section of an FM receiver, and the resultant audio signal is applied to the Y plates of the crt in the RadiVet, a wobbulator display of either the IF filter characteristics or the discriminator or ratio detector characteristics may be obtained. The effect of trimming these circuits can be observed and the circuits aligned for optimum performance very rapidly. If a ratio detector is being aligned, since it is possible to provide simultaneous AM at a higher frequency, the wobbulator display so obtained enables the circuit to be set up correctly for optimum rejection of AM. A similar procedure, using a very much lower frequency sweep, can be applied to give the response characteristics of a normal AM receiver IF filter. 1.2. Audio Oscillator An audio oscillator providing a choice of eleven fixed frequencies between 40 c/s and 15 kc/s is incorporated in the RadiVet. This oscillator may be used for amplitude or frequency modulation of the RF oscillator, as an audio output signal for tests on audio equipment and tape recorders and to scan the X axis of the cathode ray tube. RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 9 OF 37 www.TheValvePage.Com 1.3. Oscilloscope The crt has an associated DC coupled Y amplifier and time-base. The frequency response extends from DC up to 1 mc/s and in conjunction with the saw-tooth time-base generator, provides a useful oscilloscope for general waveform investigations. The Y attenuator is calibrated, and in conjunction with a calibrated Y-shift control, enables the amplitude of any observed waveform to be measured. 1.4. DC valve voltmeter The cathode ray tube, calibrated “Y” attenuator, and calibrated “Y-shift” control form a DC valve voltmeter which enables voltages to be measured without placing an appreciable loss on the circuit. This is particularly useful when measuring the potentials of valve electrodes, where an appreciable current drawn by the measuring instrument can completely change the voltage and provide very misleading results. 1.5. AC Valve Voltmeter As mentioned in the paragraph dealing with the oscilloscope facility above, the amplitude of a waveform displayed on the crt may be measured by means of the Y attenuator and calibrated Y- shift control. The input impedance is high, as in the case of DC measurements, and the instrument therefore operates as an AC valve voltmeter at 50 c/s and audio frequencies. 1.6. Frequency Calibrator The instrument contains a 5 mc/s crystal oscillator that may be used to calibrate the output frequency to a very high degree of accuracy. 1.7. Suitability for AC/DC receivers The chassis and earth line of the RadiVet are isolated from earth and from the case, and the instrument may therefore safely be used with AC/DC sets where the chassis may be live relative to earth. 2. OPERATION 2.1. Initial Adjustment The RadiVet is supplied complete and ready for use. All probes are permanently connected, and a mains lead is provided to which a plug should be connected. The red, black and green leads are live, neutral and earth respectively and it is important that the earth lead should be connected to ensure correct screening. The RadiVet is despatched with the mains tapping panel set for operation on 230 volt supplies. If operation on supplies of different voltage is required, the fused plug on the tapping panel, which is accessible inside the right-hand probe storage aperture, should be moved to the required tap. 2.2. Frequency Calibration If the full accuracy of the frequency calibration of which the RadiVet is capable is to be realised, it is necessary before use to reset the scale by means of the trimmer C75, which is located in the right- hand compartment of the case, as shown in Fig. 2. It is also desirable, where freedom from drift is essential, (for instance when operating on the Long and Medium broadcast bands) for the instrument to have been switched on for a period of at least twenty minutes. The normal procedure for crystal calibration is as follows:- (a) Set the tuning dial accurately to the check-point nearest to the frequency at which the instrument is to be used. The check-points at 2.5 mc/s intervals are recommended for normal use. Additional points which occur at very much reduced amplitude every 5/3 and 5/4 mc/s are not reliable and should not be used unless their identity has been fully established. Both scales are linearly calibrated in 1 mc/s steps only, whilst the number of kc/s are read off the subsidiary scale RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 10 OF 37 www.TheValvePage.Com calibrated in 1 mc/s steps only, whilst the number of kc/s are read off the subsidiary scale which is calibrated at 10 kc/s intervals and revolves once for every 1 mc/s. Reference should be made to Fig. 4.which shows the tuning dials. The example illustrated could be:- or 4.425 mc/s 9.425 mc/s 14.425 mc/s 89.425 mc/s 94.425 mc/s 99.425 mc/s depending on the setting of the RANGE switch (which determines which of the three scales is in use) or the setting of the OUTPUT switch (which determines whether 85 mc/s is to be added to the scale reading). Where a crystal check-point coincides with a wanted frequency, the accuracy will be 0.01% but between check points the accuracy will be better than 40 kc/s. (b) Set the OUTPUT switch to XTAL CHECK, the GAIN switch to INT. CHECK, and the FM and AM switches to OFF. The X PLATES switch may be at 50 c/s or any of the four TB ranges but not at VAR. FREQ. since the audio oscillator is operating as an amplifier for this facility. (c) Rotate the trimmer C75, the location of which is shown in Fig. 2., until a deflection is obtained on the Y axis of the crt. The amplitude of the deflection may then be adjusted to a convenient height by means of the RF OUTPUT control. As the trimmer is adjusted through the correct tuning point the amplitude of the deflection will gradually rise to a maximum and then suddenly fall to zero. If adjustment is continued in the same direction the amplitude will rise equally suddenly and will then gradually fall off again. The correct setting is at the zero beat between the two amplitude peaks, but it must not be expected that this position will be completely stable and it will be sufficient if the beat is obviously of an audio frequency. When the OUTPUT and GAIN switches are returned to the required setting the correct output frequency will be obtainable at Probe A (RF probe). When the wobbulator facility is required the above adjustment should be made but before altering the setting of the GAIN and OUTPUT switches, the FM switch and the X plate switch should be set to 50 c/s and the DEVIATION control advanced. The beat note will be seen to become localised at the centre of the trace into a small pip. The frequency is now being swung at 50 c/s in synchronism with the X plate scan and every time the frequency of the variable frequency oscillator is equal to that of a crystal harmonic this pip is produced. This point on the trace must now be identified since the pip vanishes when the instrument is in normal use and in any case its retention would only serve to confuse the outline of any characteristic being traced. To do this, it is necessary to bring the pip exactly under the vertical graticule, using the X shift control. Thereafter the point on the trace that appears under this graticule is at the frequency shown on the dial. The GAIN the position being selected to provide reasonable amplitude on the crt. The X PLATES switch should be turned to one of the four T.B. positions. The position chosen will depend on the frequency of the signal being observed and should be the one that enables a steady picture to be obtained at some position of the TB VEL. FINE control. When a steady waveform of reasonable amplitude is obtained, adjust the BRILLIANCE and FOCUS controls to obtain a sharp trace and centralise the display by means of the X shift and Y shift controls. 2.7. Valve Voltmeter DC Voltage measurements may be made by means of the crt, the calibrated Y attenuator, and the Y shift control. When making measurements on AC/DC receivers, care should be taken to ensure that RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 13 OF 37 www.TheValvePage.Com Probe A and B are not stowed or located in any position where the leads may short circuit to earth or be a danger to personnel. The X PLATES switch should not be switched to VAR.OSC. if the OUTPUT switch is at XTAL CHECK. With Probe C short circuited, set the trace on the central horizontal graticule with the Y SHIFT VOLTS control and note the outer scale reading of the Y SHIFT control. Set the GAIN switch to the desired DC range as follows:- DC:- 0 - 20v DC x 10 0 - 60v DC x 30 0 -. 200v DC x 100 0 - 600v DC x 300 0 -2000v DC x 1000 Connect Probe C to the point at which the voltage is to be measured. A deflection of the trace upward for a positive voltage and downward for a negative voltage will be observed. The trace should be brought to the central line with the Y SHIFT VOLTS control and the reading noted. The difference between the two readings multiplied by the GAIN setting gives the voltage. For example:- First Reading - 0.1v Second Reading + 0.9v Difference = + 1.0v GAIN setting = x 30 Voltage = 1.0 x 30 = +30v 2.8. Valve Voltmeter AC 2.8.1. AC Voltage below 400 peak-to-peak The connections are the same as for the preceding Section 3.7 except that it is not necessary first to check the zero setting. Measurement may be made at frequencies between 30 c/s and 100 kc/s and at frequencies up to 500 kc/s with reduced accuracy, using the following switch positions:- 0 - 0.7 v RMS AC x 1 0 - 2.0 v RMS AC x 3 0 - 7.0 v RMS AC x 10 0 - 40 v RMS AC x 30 0 - 140 v RMS AC x 100 First move the trace with the Y SHIFT VOLTS control so that its top is coincident with the central horizontal graticule and note the reading of the INNER scale. Then move the trace until its bottom is coincident with the central horizontal graticule and note the new reading. Add the two readings together (ignoring the +ve and ve signs) and the result, multiplied by the GAIN switch setting, is the RMS value of the voltage. For example:- First reading - 0.6v Second reading + 0.6v Switch setting AC x 100 Voltage = (0.6v + 0.6v) x 100 = 1.2 x 100 = 120v AC RMS RadioFans.CN 收音机爱 好者资料库 AIRMEC RADIVET MODEL 211 PAGE 14 OF 37 www.TheValvePage.Com 2.8.2. 50 c/s Voltage above 400 peak-to-peak In addition to the AC readings dealt with in Section 3.8.1, higher voltages at a frequency of 50 c/s and having no superimposed DC may be measured with the Y GAIN control in the DC positions. The general procedure is the same as for 3.8.1 and the voltage ranges are:- 0 - 7v RMS DC x 10 0 - 20v DC x 30 0 - 70v DC x 100 0 - 400v DC x 300 0 -1400v DC x 1000 3. TESTS ON FM RECEIVERS 3.1. I.F. Response Service manuals may call for either the single spot frequency or wobbulator method of alignment, but whichever method is used, it must be remembered that most modern FM receivers incorporate a limiter. The signal input level should be kept as low as possible and must always be less than the minimum necessary to operate the limiter. Even if a high level limiter, such as is employed with a ratio detector is encountered, the same warning still applies. 3.1.1. Spot Frequency Alignment Probe or Control Connecting or setting Probe A. (RF) Probe B (Audio) Probe C (Oscilloscope) FM AM AUDIO OSC. GAIN PLATES TUNING RF FREQ. RANGE OUTPUT Signal grid of frequency changer Not used Live side of volume control (see text) OFF VAR. FREQ. Any suitable frequency; say 1 kc/s AC x 1 50 c/s or any of the 4 TB positions * Receiver intermediate frequency