HP-Service-Note-412A-4 电路图.pdf

41 2 A-4 MODEL 412A/AR Dc VACUUM TUBE VOLTMETER SERIAL 004-03632 AND BELOW BIAS CIRCUIT IMPROVEMENTS To further increase the reliability of your Model 412A/AR DC Vacuum Tube Voltmeter - particularly at low line voltages (less than 115 volts) - two changes in the bias supply circuitry are recommended. In the Model 412A, serial 004-03632 and below, silicon diode CRlOl should be replaced by Stock No. G-29G-79, a silicon diode having improved power capabilities. In serial 004-02882 and below, R122, a 560 ohm 1 watt resistor, should also be changed to 120 ohms, 1 watt, After completing the modification, adjustment of your Voltmeter is required as outlined below under “Adjust- ment Procedure”. PARTS REQUIRED FOR MODIFICATION Quantity Description St&k No. 1 Resistor, fixed, composition, 120 ohm, &lo%, 1W for R122 . , 0690-1211 1 ( $ 9 Diode, Silicon, for CRlOl . G-29G-79 L MODIF IC AT ION PROCEDURE 1) Discoiinect power and remove cabinet, 2) In serial 004-03632 and below: Change Silicon Diode, CR101, located below the De AMPLIFIER OUTPUT connector at rear of instrument and on line cord side, to a G-29G-79 Silicon Diode. 3) In serial 004-02882 and below: Replace R122, a 560 ohm 1 W resistor, located between pin 2 of V103 and tap 2 on Power Transformer, T1, witha 120 ohm, 1 W resistor. 4) Replace cabinet, ADJUSTMENT PROCEDURE Bias adjustment should be performed as outlined in Section IV, of the Operating and Service Manual for your instrument. distribution abcfg4 01223-1 RadioFans.CN 收音机爱 好者资料库