Brüel & Kjær 2619 1/2" Preamplifier Service Instructions
Nærum - Denmark
Consisting of:
- Electronic Section (2619.1)
- Position of Components (2619.2)
- Parts List (2619.3)
- Circuit Diagram (2619.4)
Refer to exploded view (2619.2) for instructions on how to open the Preamplifier Type 2619.
Trouble Shooting
If a fault is not obvious (e.g., faulty transistor, broken resistor), first test DC voltages and compare them with the voltages shown in the tables to localize the defect. If this method is unsuccessful, check the instrument using the adjustment procedure described. After a fault is remedied, recheck voltages and adjustments influenced by the repair.
Tolerances in these instructions are guides for adjustment and control. Deviations should not be corrected without ensuring that the test instruments used have sufficiently small tolerances to avoid influencing measurements.
These instructions are for servicing minor faults. Significant deviations requiring special control equipment and experience should be handled by the factory.
Spare Parts
When ordering spare parts, please state the apparatus type and serial number.
Instruments Necessary for Service and Repair
- Multimeter (50 μA)
- Beat Frequency Oscillator type 1022 (1013)
- Frequency Analyzer type 2107
- Pistonphone type 4220
2619.1 Electronic Section
1.1. DC Voltages
When type 2619 is connected to a 120 V DC supply:
- Voltages on Guard Ring: 60 V ±5 V
- Voltages on V₁ emitter: 65 V
- Voltages on V₁ collector: 60 V
- Heating Element: approx. 50 mA
- V₃ collector: 120 V
- V₃ emitter: 65 V
1.2. Function Check
Procedure a: Place the Pistonphone 4220 on the microphone input of the Preamplifier 2619 and switch 4220 to "Measure". The indication on the Microphone Amplifier (2107) should match the Sound Pressure Level produced by the pistonphone (correct for the "K" factor).
Procedure b: If a pistonphone is unavailable, feed a 1 V, 1 kHz input signal through the input adaptor JJ 2615 to the preamplifier 2619 and check the output voltage is 1 V.
1.3. Attenuation
Using a 120 V DC supply or 28 V DC supply:
Procedure a: Check the sensitivity of the Microphone Amplifier type 2107 in "Condenser Microphone" and "Direct" positions. Adjust deflection to the red mark using "Sen. Cond. Micr." and "Sen. Ampl. Input" if necessary. Connect a 1000 Hz input signal to the Microphone Amplifier 2107 INPUT and adjust the input voltage for 1 V deflection.
Procedure b: Connect a 6 pF capacitor in series with the input signal. Feed the signal to the gold contact on the front of the 2619 and measure the attenuation of the output voltage. Maximum attenuation should be 1 dB. Change the frequency to 10 Hz and repeat the check; maximum attenuation should be 4 dB.
1.4. Frequency Response
Procedure a (28 V DC supply): Input signal: 100 mV, 1 kHz connected via JJ 2615. Check frequency response from 2-200,000 Hz.
- Frequency: 3 Hz, Tolerance re. 1 kHz: -3 dB
- Frequency: 1 kHz - 150 kHz, Tolerance re. 1 kHz: ±2 dB
- Frequency: 200 kHz, Tolerance re. 1 kHz: ±0.5 dB
Procedure b (120 V DC supply): Input signal: 100 mV, 1 kHz connected via JJ 2615. Check frequency response from 2-200,000 Hz.
- Frequency: 2 Hz (adjustable by R1), Tolerance re. 1 kHz: -1 to -3 dB
- Frequency: 1 kHz - 150 kHz, Tolerance re. 1 kHz: ±0.2 dB
- Frequency: 200 kHz, Tolerance re. 1 kHz: -1 dB
1.5. Distortion
Procedure a (28 V DC supply): Frequency: 1000 Hz. Adjust input voltage for 4 V output from 2619. Distortion: Max. 4%.
Procedure b (120 V DC supply): Measure distortion again at 32 V output voltage. Distortion: Max. 4%.
1.6. Noise and Hum
Using a 28 V DC supply or 120 V DC supply:
Screw the input adaptor JJ 2615 onto the preamplifier and connect the input of the JJ 2615 to ground.
- Noise (Linear, 20-40,000 Hz): 20 μV
- Noise (Curve "A"): 4 μV
2619.2 Position of Components
This section details the physical placement of components on the printed circuit boards. It shows layouts for the Output Stage (ZE 0025) and Input Circuit (ZE 0023) with reference to printed circuit XC 0411. Specific component locations are indicated by reference designators on diagrams.
The diagrams illustrate connections for various voltage inputs (6V, 200V, 12/28V, 120V) and signal paths, including transistors (Q1, Q2, Q3), capacitors (C1, C3, C4, CB), resistors (R1, R13, etc.), and the core screen.
Exploded View
The exploded view diagram illustrates the physical assembly of the 1/2" Preamplifier Type 2619. It shows various sub-assemblies and components, with arrows indicating the direction of rotation required to disassemble the housing. Components are identified by alphanumeric codes (e.g., ZE 0024, DB 1351, YJ 0046).
2619.3 Parts List
| CIRCUIT DIAGRAM REF. | COMPONENT TYPE | STOCK REF. |
|---|---|---|
| CAPACITORS: | ||
| C1 | Tantalum | 6 µF / 10 V CF 0007 |
| C2 | Glas | 300pF / 300 V CG 0002 |
| C3 | Ceramic | 0.1 µF / 50 V CK 5100 |
| C4 | Polystyrene | 47 nF / 250 V CS 0550 |
| RESISTORS: | ||
| R1 | Carbon 0.2 W 5% | 1.2 kΩ RB 3120 |
| R2 | Carbon 0.2 W 5% | 4.7 kΩ RB 3470 |
| R3 | Carbon 0.2 W 5% | 8.2 kΩ RB 3820 |
| R4 | Carbon 0.2 W 5% | 27 kΩ RB 4270 |
| R5 | Carbon 0.2 W 5% | 33 kΩ RB 4330 |
| R6 | Carbon 0.2 W 5% | 56 kΩ RB 4560 |
| R7 | Carbon 0.2 W 5% | 220 kΩ RB 5220 |
| R8-12 | Metal 0.25 W 10% | 200MΩ RH 0905 |
| R13 | Carbon 0.2 W 5% | 18 Ω RA 0300 |
| SEMICONDUCTORS: | ||
| V1 | Silicon Transistor 2N4289 PNP | VB 0049 |
| V2 | Silicon Transistor 2N4292 NPN | VB 0050 |
| V3 | Silicon Transistor 2N3440 NPN | VB 0250 |
| V4 | F.E.T. U 2002 | VB 0505 |
| Q1 | Silicon Diode IN681 275 V / 30mA | QV 0209 |
| Q2,3 | Silicon Diode EC401 100 V / 225mA | QV 0213 |
| PRINTED CIRCUITS: | ||
| Input Circuit | XC 0411 | XC 0411 |
| Complete with components | ZE 0023 | |
| Complete with FET input and heating element | ZE 0024 | |
| Output Stage | XC 0007, XC 0008, XC 0009, XC 0010 | |
| Output Stage, complete with comp. and plug | ZE 0025 | |
| Cable | AO 1003 | |
2619.4 Circuit Diagram
The circuit diagram shows the schematic for the 1/2" Microphone Preamplifier Type 2619. It details the input and output stages, including transistors (V1, V2, V3, V4), diodes (Q1, Q2, Q3), resistors (R1-R13), and capacitors (C1-C4). The diagram illustrates signal flow and component interconnections, including power supply inputs (200V, 150V DC, 28V DC, 6V) and a heating element.
A note specifies that if driven from a 28 V DC supply, pins 5 and 6 should be short-circuited.
The diagram also includes connection pinouts for the external connector, indicating functions such as Ground, Signal, Supply Voltages, and Heating Element.
