The most sophisticated of the Unilab Retro range, the Regulated Lockable Power Unit offers smooth, regulated d.c. at 2, 4, 6, 9 or 12 volts, at up to 4 amps. This unit is for specialist requirements, such as electronics, or where a constant voltage is required under variable load. The voltage is selected using a five-position switch, and can be locked either at a particular voltage, or within a range of voltages, by way of hex socket screws surrounding the selector switch. An Allen key is provided for the teacher or technician to set the desired locks. The power is output from shrouded 4mm sockets, and the shroud can be partially unscrewed for other types of connection, such as bare wires. The unit has two in-built layers of protection. The first is a thermal trip on the secondary circuit, with a reset button for when the problem load has been disconnected. The second is a 1A mains fuse, accessed from the front panel, on the primary circuit.