I made a small control board to fit inside the DSP-10 (it is nice to have some extra room) which takes the amp and relay control signals and controls the actual devices. There are two identical amp control circuits, one for the 30w brick and one for the 380w brick - a TE Systems 1452G. There are two relay circuits, one provides +13v on transmit and the other provides an isolated relay to gnd. All 4 of these are brought to the back of the DSP-10 with RCA phono jacks.

Below (click on the photos) are some photos/schematics.