LESS THAN STANDARD SEPARATION BETWEEN 2 ACR ACFT. OPERATIONAL ERROR.

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WE; ACR X; DEPARTED DFW RWY 35L WITH CLRNC TO 10000' HDG 360 DEGS. APPROX 20 NM N OF DFW WE WERE CLRED TO A HDG OF 090 DEGS TO INTERCEPT THE DFW 078 DEG R OUTBND ON THE DALLAS 6 DEP. DURING FURTHER CLB TO 17000' THE CTLR ON FREQ 132.85 DIRECTED OUR ATTN TO ACR Y CLBING OUT AT OUR 1-2 O'CLOCK POS. WE ACQUIRED VISUAL CONTACT AND IT WAS OBVIOUS WE WOULD PASS APPROX 1000' ABOVE AND BEHIND ON A CONVERGING VECTOR. WE WERE CLRED TO FL230 AFTER CALLING VISUAL CONTACT WITH ACR Y. PASSING APPROX FL180 WE WERE GIVEN A RIGHT TURN OFF THE 078 DEG R TO A HDG OF 120 DEGS AND IMMEDIATELY RETURN TO FL180; ACR Y APPEARED TO BE ON A CONVERGING VECTOR WITH US. ACR Y LEVELED AT FL190 WITH A VECTOR INSURING A DIVERGING COURSE. MY CAPT HAD ACR Y IN SIGHT AT ALL TIMES AND NEVER CAME CLOSER THAN 3 NM. THIS RPT IS FOR RECORD ONLY; BUT IT DOES REINFORCE BASIC RULES OF AVIATION. KEEP THE OTHER GUY IN SIGHT IN ORDER TO MAINTAIN A SAFE SEP. DON'T RELY ON CTLRS TO MAINTAIN SEP. I SUSPECT ACR Y WAS GIVEN AN INTERCEPT VECTOR FOR 067 DEG R ON THE DALLAS 6 BUT WAS NOT CLRED TO DO SO. HE WAS SET UP FOR A CONVERGING VECTOR. SUPPLEMENTAL INFO FROM ACN 80999: WE PASSED ABEAM ACR Y APPROX 3 NM BOTH CLBING THROUGH FL180 FOR FL230. HIS ALT WAS VERBALLY CALLED WITHIN 500' VERT OF OURS.