LESS THAN STANDARD SEPARATION BETWEEN CORP JET ARR AND COMMUTER DEP. OPERATIONAL ERROR.

Narrative

I WAS TRNING A RADAR DEVELOPMENTAL ON ARR/DEP W. THE CTLR WORKING THE HDOF POS HAD COORDINATED A NON STANDARD DEP HDG FOR 2 ACFT AND DIDN'T TELL US. CORP X WAS BEING VECTORED FOR A VIS APCH TO RWY 32 AT 4000'. COMMUTER Y DEPARTED RWY 32 AND TURNED LEFT AS ASSIGNED TO HDG 180 DEGS CLBING TO 3000'. A PREVIOUS NON STANDARD DEP HAD DEPARTED 2 MINS EARLIER AND HAD OUR ATTN. ACFT Y WAS RADAR IDENTED AND INSTRUCTED TO CLB TO 6000' AND TO EXPEDITE CLB. I THOUGHT THAT ACFT Y TYPE IN THE CLB WOULD BE MUCH SLOWER THAN CORP X ON VECTORS AT 4000'; BUT X HAD ALREADY REDUCED TO ITS APCH SPD. I INSTRUCTED THE TRNEE TO TURN X TO A 140 DEG HDG FROM ITS ASSIGNED HDG OF 110 DEGS. THAT WAS NOT ENOUGH TO ENSURE SEP; SO I OVERRODE THE FREQ AND TURNED Y RIGHT TO 230 DEGS TO PASS BEHIND X. I SHOULD HAVE ACTED SOONER; BUT I THOUGHT IT MIGHT HAVE WORKED; ESPECIALLY IF X WAS FLYING A NORMAL EXPECTED DOWNWIND SPD. ALSO; HAD THE HDOF CTLR INFORMED US OF THE GAME PLAN WE WOULDN'T HAVE BEEN CAUGHT OFF GUARD. TFC AT THE TIME WAS MODERATE. OUR RADAR IS THE TPX-42; WHICH IS NON PROGRAMMABLE AND DOESN'T HAVE C/A OR GND SPD; BOTH OF WHICH WOULD HAVE BEEN A BIG HELP. BOTH ACFT WERE ON IFR FLT PLANS AND DESERVED BETTER SVC THAN THIS.