The only parts required are:

• 1 telephone socket doubler of the correct type.
• 1 150 ohm resistor.
• 1 battery snap connector.
• 1 PP3 type 9 Volt battery, aka 6LR61, MN1604, 6F22, RX22 etc.

Required Tools:

• Soldering iron and solder.
• Wire cutters and stripper.
• Crosshead screwdriver.

For notes on choosing a suitable socket doubler and the preparation it requires, click here. (You may disregard the information about cutting tracks and attaching wires.)

Assembly

With the doubler dis-assembled and the plug discarded, feed the two wires from the battery snap, through the hole left by the removed plug in the back half of the doubler. To prevent the wires being pulled out, make a knot at a suitable point along the wires. The pcb inside the doubler, links each pin of one socket to the corresponding pin on the other socket. It is necessary to make solder connections to the tracks linking pins 2 and 5 of each socket. Solder the black wire to any point on the pin 2 track. The red wire must be connected to one side of the 150 ohm resistor. The other side of the resistor must be connected to the pin 5 track. The pcb may have some un-committed mounting holes which will accommodate the resistor and any necessary wire links to it. To provide convenient soldering points, it may be necessary to scrape away carefully the solder resist covering the tracks. If no mounting holes are available, just epoxy the body of the resistor to the board, at a location which will not obstruct re-assembly. When the connections are satisfactory, re-assemble the doubler.

Operation

As this unit provides no dialtone or ring signal, equipment linked by it must be used accordingly. Modem and fax software must be set either not to wait for a dialtone prior to dialling, or to go online using an existing connection. Similarly fax machines or fax modems must be used in the manual send or receive mode as appropriate.
Immediately after use, to prevent battery drain, disconnect devices from both sockets.
The unit may be stored with the battery connected, as no current is drawn.