Is the new RailBoss 4 TX compatible with my old hobby receivers?

Unfortunately, no. All 2.4GHZ radio systems are different. Each manufacturer,  uses their own protocol, often to avoid patent infringement, So just like Spektrum parts won't work with Futaba, the RailBoss 4 radio won't work with any of your hobby style receivers.

So if you have the RailBoss "Hobby" system (one that uses stick transmitters), and you want to upgrade to RailBoss 4, neither your old RailBoss board nor you hobby receiver can be used with RailBoss 4. You will need to purchase both the RailBoss 4 transmitter and a RailBoss 4 integrated receiver/control board.

Some of the huge improvements RailBoss 4 offers over the old hobby system ...

• TX fits in your pocket.
  
• No on/off switch on the TX.
  
• No waiting for the TX and RX to link up.
  
• No separate RX to wire to the control board.
  
• No throttle calibration to mess with.
  

New functions ...

• You can control 2 Phoenix Sound Remote Un-Couplers directly from the RailBoss 4 (no Phoenix interface board required) 
  
• With two RailBoss 4 systems, you can run two trains on the same loop, both making random station stops, and they will automatically maintain spacing. This is possible because each train actually has bi-directional communications. They talk to each other.
  
• Optional 10 amp motor driver available.