HP-Service-Note-400D-4B 电路图.pdf

《HP-Service-Note-400D-4B 电路图.pdf》由会员分享，可在线阅读，更多相关《HP-Service-Note-400D-4B 电路图.pdf（3页珍藏版）》请在收音机爱好者资料库上搜索。

1、- - - 2 b 400D-46 MODEL 400D/H VACUUM TUBE VOLTMETERS 400D serial 17970 and below, 400H serial 2237 and below REDUCTION OF RESIDUAL NOISE MODIFICATION KIT STOCK NO. 400D-95B Residual noise indicated by the meters in the above instruments can be reduced by a modificationof the in- put attenuator. A h

2、igher degree of residual noise re- duction is obtained on the upper voltmeter ranges by this modification. The input attenuator is changed from a capacity divider to a resistive divider system by the addition of a kit of parts available under Stock No. 400D-95B. All circuit changes are made on the I

3、nput Attenuator Resistor Board that is mounted directly behind the front panel INPUT terminals, A frequency response adjustment outlined in these Service Notes will be required after this modification has been completed. PARTS FURNISHED IN THE 400D-95B KIT L Quantity 1 1 2 1 1 1 1 1 Description Stoc

4、k No. Matched set of three resistors , . . , . . . . , . , , 400D-67 Capacitor, fixed, molded tubular, paper, 0.047 pf, ilvo, 600vdcw . . , . . I . . . . . . . . . . . . . 0160-0005 Resistor, fixed, composition, 10 ohms, f lo%, 1/2 watt 0687-1001 Resistor, fixed, composition, 27 ohms, f lvo, 1/2 wat

5、t 0687-2701 Resistor, fixed, composition, 100 ohms, c3 -c5 .OIpF -4700 t, 7 - 400D-4B Page 3 CHANGES IN OPERATING AND SERVICING MANUAL The procedures given in the manual for calibration AFTER INSTALLATION OF 400D-95B MODIFICA- and frequency response adjustment should be disre- TION KIT IN AN MODEL 4

6、00D OR 400H VACUUM garded and any adjustments should bemade as given below. The data in the manual is still valid regarding equipment required and accuFacies necessary. Make the following changes in the parts list L TUBE VOLTMETER Change C2 from .01 pf to: capacitor, fixed, paper dielectric, ,047 pf

7、, j lvo, 600 vdcw; Stock NO, 0160-0005. Change R2 from 1000 ohms to: resistor, fixed, composition, 100 ohms, j lvo, 1/2 watt; Stock No. 0687-1011. Change R3 from9100 ohms to 10.31K and R4 from 10 megohms to 10.3M: Matched resistor set; Stock No, 4001)-67. Delete resistor R5. This resistor is replace

8、d by a wire jumper during the installation of the modi- fication kit, Add resistor R86 resistor, fixed, composition, 47 ohms, h lqo, 1/2 watt; Stock No. 0687-4701. CALIBRATION PROCEDURE CAUTION: If the setting of C4 has been disturbed, an approximate rough setting can bemade by adjusting it so that

9、the solder globule is at 3 oclock, which is approximately 1/2 capacity. 1) Feed a 400 cps 0.300 volt signal into the meter. Adjust R29A so that the meter reads exactly 0.300 volt, If the adjustment of C4 has not been disturbed, the instrument should now be calibrated properly on all ranges. A check

10、on the calibration can be made by proceeding as follows, 2) Feed 400 cps at 1,000 volt into the meter with a monitoring device connected in parallel with the meter input that has a flat frequency response preferably from 10 cps to 6.5 mc. No:e the reading on the monitor. 3) Increase the input freque

11、ncy to 20 kc. Adjust the signal level until the monitor indicates the same value of signal as before (l,ooo volt). MAKE VOLTMETER SCHEMATIC DIAGRAM AGREE WITH THE FOLLOWING PARTIAL DIAGRAM -. i / 4) The instrument should still read 1,000 volt. If it does not, the setting of C4 is not correct and sho

12、uld be adjusted slightly to bring the meter pointer onto the exact reading. 5) Check the calibration of the 1OOO:l division by feeding in 400 cps signals of exactly 0.300 volt and 1.000 volt. Both voltages shouldgive exactly full scale deflections on their respective ranges, If they do not, the prec

13、ision 1OOO:l resistive divider is off, If 0.3 volt is correct and 1.0 volt is reading high, decrease the value of the pad in parallel with R3. If 1.0 volt reads low, increase the value of the pad in parallel with R3. FREQUENCY RESPONSE ADJUSTMENTS The adjustments for frequency response are somewhat

14、similar to the manual but should be adjusted in the following sequence and at the frequencies specified. 1) Set the frequency response on the 0.1 volt range at mc with c21, 2) Set the frequency response on the 0.01 volt range at mc with c16. The 1OOO:l input voltage divider which is switched into th

15、e input circuit for the one-volt range and above, has been changed from a capacitive to a resistive type divider. The 1000 1 voltage division is now determined at audio freauencies mainly by factory matched re- 3) Set the frequency response on the 1.0 volt range at 2o kc with c4. sistors R3 and R4 a

16、nd very- slightly by C4 which flattens the response of the 1OOO:l divider at higher frequencies, C4 also affects the calibration of the one-volt range and above even at low audio frequencies Le.: 400 cps. The calibration process now becomes a part of the fre- quency-compensation adjustment process,

17、Trimmer C4 has been properly set at the factory and should never need adjustment, If C4 is accidently disturbed the accuracy of the meter will be destroyed except at very low audio frequencies, 4) Set the frequency response on the 1.0 volt range at 4 mc by adjusting the value of R6. 5) Set the frequency response on the 3.0 volt range at 4 mc with C14. 6) The instrument should now be calibratedcorrectly for any frequency on any range. 00668-2 RadioFans.CN 收音机爱 好者资料库