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Assembly
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  • 845 tube amplifier assembly instructions
    Page 2 of 2
    Main | 1 | 2 |
    2. Soldering components
    Follow the marking on PCB and solder the components accordingly. As the rules of thumb, start from the lowest component first (such as resistors). Be aware of the polarity when you're soldering the electrolytic capacitors. As for Auricap, even though they have no polarity on the capacitors but it is advisable to follow the manufacturer instructions: the black lead is "in" and the red lead is "out". Don't solder the preamp tube sockets onto the PCB yet.

    Note: To avoid "dry-joints", make sure you heat the component leads and the soldering points together. Apply solder and keep heating until it flows and covers both the soldering points and component leads. (Be careful of your soldering timing. Don't overheat the components.)
    2 Watt Resistors
    2 Watt Resistors
    Power Supply
    High Voltage Delay Circuit
    3. Installing milliamp meter
    Use 3mm screws and washers to install the milliamp meter to the front panel of the chassis.
    4. Assembly the chassis
    Use the 4mm screws to assembly the chassis.
    5. Installing binding posts, RCA jack, power supply socket and fuse holder.
    There should be 1 black and 2 red binding posts for each channel. The black one is for "0" and the red ones are for 4 ohm and 8 ohm respectively.
    6. Installing preamp tube sockets
    Use the socket holders and screws to hold the preamp sockets under the top-panel.
    7. Mounting the preamp PCB.
    Mount the PCB onto the brass spacers. Make sure all the socket pins come through the PCB. Secure the position of the PCB with screws and then solder the preamp sockets.
    8. Installing W101 and W201 AC balance potentiometer.
    Install W101 and W201 AC balance potentiometer under the top panel and turn it down to zero.
    9. Install 845 tube socket.
    Fix the 6mm spacer to 845 tube socket first and then mount the tube socket to the top-panel.
    845 Tube Socket
    10. Mounting the power supply PCB.
    Put two spacers on top of each other and mount the power supply PCB on the brass spacers.
    11. Connecting the wires.
    Find the connectors on the PCBs and connect them accordingly.
    12. Connecting the cathode bias potentiometer.
    See picture.
    13. Connecting the AC balance potentiometer.
    See picture.
    14. Testing
    a) Check and confirm that all components and connections are installed correctly, especially those components with polarity. This is very important as you are dealing with a very high voltage circuit. A simple mistake can be very costly and dangerous.
    b) Insert all vacuum tubes. The 845 tubes are bayonet mount. Insert the tube and turn left to lock the tube.
    c) Put a 3.15A fuse into the fuse holder.
    d) Turn W101 and W201 to about half way.
    e) Connect the speakers. Check the impedance of your speaker. Most speakers are 4 or 8 ohm. If your speakers are 6 ohm, you can use the 0-8 ohm configuration.
    f) Turn the power on. All vacuum tubes should light up. Wait about 1 minute, the high voltage circuit will switch over and the blue LED should switch on.
    g) Read the miliamp meter and turn the W102 and W202 to set the bias current to about 85-90mA for both channels.
    h) Adjust the W101 and W102 until the humming becomes inaudible.
    i) Set the multimeter to mV and measure the voltage. Turn the AC balance potentiometer until you get the smallest value. The normal value should be about 5mV.

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