GENERAL RADIO COMPANY 620-A Maintenance Instruction Book Download Page 6 | Manualshive

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Summary of Contents for 620-A

Page 1: ......

Page 2: ...GENERAL RADIO COMPANY FIGURE 1 FIGURE 2 ...

Page 3: ...egacycle 10 kc The auxiliary scale on the driving shaft effec tively subdivides each main scale division into 10 parts Each auxiliary scale divi sion is therefore 1 kilocycle The fre quency for any scale setting is given by the sum of the coil switch reading and the reading or the dial For example in Fig ure l and Figure 2 the frequency is 14 496 Me PART 2 INSTALLAT InN SHIPPING LIST With each Typ...

Page 4: ... tioned above occur at several points along the scale These intermediate points occur where a harmonic of the heterodyne beats with a crystal harmonic For exam ple the second harmonic gives a zero beat setting at l 2 scale or 0 5 Me the third harmonic gives zero beat points at l 3 and 2 3 scale corresponding to 0 33 and 0 66 Me the fourth harr onic gives points at 0 25 0 50 and 0 75 Me and so on F...

Page 5: ...uency is picked up For example suppose a fre quency near 60 Me is to be measured En terin Figure 4 at 60 on the frequency scale an intersection on line 3 Coil 19 condenser maximum is found Progressing further upward an intersection on line 4 Coil 15 condenser zero is obtained Simi larly line 5 Coil 12 condenser zero line 6 Coil 10 condenser 0 Any one of these settings gives a harmonic at 60 Me bei...

Page 6: ...harmonic numbers to be deter mined without ambiguity Knowing the num bers of the harmonics corresponding to any zero beat point it is possible to improve 4 the accuracy of measurement by taking the difference in frequency of two zero beat points which are separated by several har monics then dividing this difference by the number of harmonic intervals between the two observed zero beat points or t...

Page 7: ... pickup particularly if a high harmonic must be used in t he measurement 5 Another method of obtaining a signal strong enough to be measured is to use an aUY iliary oscillator whose fundamental is set to a harmonic of the transmitter fre quency and to measure a harmonic of this oscillator In measuring ultra high frequency transmitter s located at some distance from the heterodyne an exposed coupli...

Page 8: ...GENERAL RADIO COMPANY FIGURE 3 6 ...

Page 9: ...GENERAL RADIO COMPANY FIGURE 4 7 ...

Page 10: ...GENERAL RADIO COMPANY FIGURE 5 8 ...

Page 11: ...GENERAL RADIO COMPANY Cl OG r r _J L FIGURE 6 Location ot Coils and Condensers 9 I QJ ...

Page 12: ...MC 10 j m II z Gl m J I I 13 I I 141 c I c I I I 1s I 0 0 I I I C l I F 0 3 tt 18 z 19 HET C AL ll FIGURE 7 Wiring Diagram for Type 620 A Heterodyne Frequency Meter and Crystal Calibrator ...

Page 13: ... 6 4000 1 R 7 7ooon R 8 18 000 n L 1 L 2 L 3 L 4 L 100 L 101 L 102 L 103 L 104 L 105 i 106 L 107 L 108 L 109 INDUCTORS Type 620 36 Nat l 100 Choke Nat l 100 ehoke Nat l 100 Choke Type 620 310 Type 620 311 Type 620 312 Type 620 313 Type 620 314 Type 620 315 Type 620 316 Type 620 317 Type 620 318 Type 620 319 SWITCHES S 1 Type 510 450 S 2 Type 139 335 S 3 Type 339A S 4 Type 139 333 This instrument i...

Page 14: ... the contacts and brushes on the rotor are clean at this time and also to see that the AC BAT switch contacts are clean Crocus cloth is recommended for cleaning these surfaces 2 0 LINE FUSES BLOWING OUT 2 1 Remove all tubes and check with new fuses If fuses hold check the tubes and then reinstall the rectifier and the other tubes one by one until the defective tube or de fective tube circuit has b...

Page 15: ...l oscillator by varying the frequency of the r f signal Snap the switches back and forth several times to see if an erratic contact may be causing the non oscillating condition Also rap the panel to check for some loose joint contact or defective tube If the heterodyne oscillator does not osc llator check the L 3 and L 4 chokes to see that they are making contact in their mountings and for open ci...

Page 16: ...or the a c and d e measurements of all voltages Values as given were obtained from a standard Type 620 A Heterodyne Frequency Meter and Calibrator that was being calibrated for stock Where operating voltages are not critical variations as great as 20 may be expected T 1 T 2 T 3 T 4 T 5 Output Function Piezo Elec tric Oscil 954 lator Heterodyne 955 Oscillator 955 Detector 955 Amplifier 84 Rectifier...

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