Thank you for your purchase of the MFJ-557 Deluxe Code Practice Oscillator. With its straight Morse key and heavy non-skid metal base, learning code is easy using the MFJ-557. The MFJ-557 uses a 9 V battery or an optional DC power supply can be connected to the power jack on the side. Instructions: Remove the top of the MFJ-557 to install the 9V battery. l. Replace the top for operation. 2. An optional 5-15 V DC power supply (MFJ-1312) can be connected to the MFJ-557. If you use your own DC power supply make sure the tip is positive. 3. Use the adjustment knobs on the top of the MFJ-557 to change the volume and tone to your preference. If private listening is desired, connect a mono or stereo earphone or headphones to the sub-miniature jack on the side of the MFJ-557 labeled "EARPHONE". 4. The straight key of the MFJ-557 can be used to key a transmitter but you may not use the MFJ-557 as a tone monitor for this purpose. The MFJ-557 must be disconnected from the straight key. Disconnect the two wires from the straight key and put them to the side. Connect the transmitter to the two lugs on the straight key. REMEMBER you will destroy the MFJ-557 if you attempt to key a transmitter while the MFJ-557 is still connected to the straight key.