By: Mark Mervine
A booster is required to operate more than about four trains simultaneously. On the used market, a 6015 or 6017 will typically sell for ~$150-200. Add in the need for another digital transformer (6001 or 6002) at ~$100 and this gets to be an expensive expansion of your digital system.
Another option is to use a Delta 6604 controller as a booster. These came with many starter sets and sell for as little as $10-15 on the used market. It can be used in combination with a 32VA starter set transformer (6646/6647). The best use of a 6604 as a booster is to power switches and signals, keeping all of the power of your digital transformer for running trains.
Below is a drawing of how to connect up the 6604. Note that the brown ground wire is interconnected between the tracks and all of the units. The red wires on either side of the 6604 must be kept isolated from each other. On the left side of the 6604, the red wire is connected to the red wire output to the tracks and the 6021. On the right side of the 6604, the red wire is connected only to signals and switches. The two gray wires (sockets labeled I & II) on the back of the 6604 must be connected together. Finally, the control switch on the 6604 must be in the rightmost or ‘stop’ position (not as shown in the drawing).
(click to Enlarge)
It is recommended that a surge protection power strip with an on/off switch be used to power both the 6001 and 6646 transformers. Thus, both the 6001 and 6646 will power up at the same time.
Please note that it is also possible to use the newer Delta 66045 controller as a booster. It should be wired up in the same fashion as the 6604. Typical prices on the used market for a 66045 are ~$25-30.