The A6X comes from the factory set for about 1.5 volts. This is good for Athearn Genesis and Ready-to-Roll locos that have the 1.5-volt bulbs, and any others with 1.5-volt bulbs. Be aware that the so called 1.5-volt bulbs used on Life-Like locos are not really 1.5-volt bulbs, but something higher: around 2 volts. Expect other Train Control Systems decoders to be made available with a regulator set for other locos' particular voltage, such as for Life-Like.

The A6X has six functions, so still has the standard unregulated voltage available for accessories requiring more than 1.5 volts.

Note: It's not the function that's regulated. It's the common that provides the voltage, so this decoder has the normal common with full voltage, and a 1.5 volt-regulated common. All the function does is sink whatever voltage is provided by whichever common you connected the bulb or device to.

For example, if connecting the 1.5-volt bulbs of an Athearn Ready-to-Roll to it, you would connect the bulbs to their normal function connections for front and rear lights, but the common for all of them will go to the 1.5-volt regulated common pad - no resistor needed.

Devices that require more than 1.5 volts are connected to their respective function pads, and to the unregulated common pad - along with whatever resistor is required, if any.

Other than the voltage regulator and having six functions, this decoder is the same as the A4X. So, if you don't need the 1.5 volt regulation or the extra two functions, you can get the A4X for less.