ARTCC RADAR CTLR CLBED A SBOUND TWIN CESSNA TO FL200 FROM FL180 AND HAD AN ACR DC9 CLBING TO FL190 NWBOUND. THE CTLR ANTICIPATED THE CESSNA BEING LEVEL BEFORE THE DC9 GOT TO FL190 AND HAD TIME TO VECTOR IF IT DIDN'T WORK. THE CESSNA SLOWED ITS CLB AND THE CTLR HAD A RADIO FAILURE ABOUT THE SAME TIME. CTLR UNABLE TO SELECT BUEC OR GET RADIO TO WORK AS THE VSCS SYS QUIT. ADJACENT SECTOR WAS ABLE TO CONTACT THE ACFT; BUT NOT BEFORE SEPARATION WAS LOST.

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I OBSERVED THIS SIT FROM D-SIDE POS. HAVING JUST BEEN RELIEVED FROM RADAR; I WAS 'CLEANING UP' BEFORE TAKING A BREAK. LOW ALT SECTOR (110-190). THE TWIN CESSNA WAS SBOUND AT FL180. THE DC9 WAS NWBOUND; CLBING OUT OF 12000 FT FOR FL190. THE TWIN REQUESTED FL200 FOR TURB. AFTER COORDINATING; RADAR CTLR CLBED THE TWIN TO FL200; PROJECTING TWIN TO BE LEVEL BEFORE DC9; AND AMPLE TIME AND AIRSPACE TO TURN ONE OR BOTH ACFT PRIOR TO POINT OF CONFLICTION. AT THIS POINT; THE FREQ FAILED; ALTHOUGH WE WERE NOT AWARE OF IT UNTIL THE TWIN APPEARED TO LEVELOFF AT FL190. SINCE THE TWIN'S ALT PUT HIM IN CONFLICT WITH THE DC9; THE RADAR CTLR ATTEMPTED TO CALL THE TWIN; THEN THE DC9; WITH NO RESPONSE FROM EITHER ACFT. AS THE DC9 LEVELED AT FL190; THE RADAR VECTOR LINES INDICATED IMMINENT LOSS OF SEPARATION; AND THE POSSIBILITY OF AN NMAC. THE VSCS INDICATED THAT WE WERE XMITTING (I TRIED TO; FROM D-SIDE); BUT LACK OF RESPONSE (RADIO AND RADAR) PROVED THAT ACFT WERE NOT RECEIVING OUR XMISSIONS. RADAR CTLR ATTEMPTED TO SELECT STANDBY EQUIP; BUT VSCS WOULD NOT ALLOW THIS. MULTIPLE ATTEMPTS BY RADAR AND DATA CTLRS TO SELECT BUEC RESULTED IN MESSAGES OF 'BUEC UNAVAILABLE.' BY GOING THROUGH OTHER SECTORS; WE HAD OTHER ACFT BROADCAST CTL INSTRUCTIONS AND FREQ CHANGES OVER OUR FREQ. DC9 PLT LATER RPTED THAT HE OBSERVED THE TWIN ON TCASII AND DID NOT BELIEVE THEY WERE A FACTOR. NOTES: AS FAR AS I CAN DETERMINE; THE VSCS RPT OF 'BUEC UNAVAILABLE' WAS IN ERROR. I HAVEN'T BEEN ABLE TO FIND OTHER SECTORS USING BUEC AT THAT TIME; LET ALONE OUR SITES. (MAINT WAS EVENTUALLY ABLE TO RETURN OUR BUEC SO WE COULD SELECT IT.) TECHNICIANS RPTED THAT OUR LINE TO THE XMITTER WAS LOST. WE GOT NO NOTIFICATION; NOR INDICATION. FREQ WAS OUT FOR 5 MINS. TWIN CESSNA CLBED 1000 FPM TO FL185; THEN 3000 FPM TO FL200. TCASII PROBABLY WOULD HAVE ACTIVATED IF ACFT HAD BEEN ANY CLOSER. WE COULD HAVE HAD A LCL TWR OR APCH CTL USE THEIR EMER RADIOS TO CALL ACFT DIRECTLY. RADAR CTLR PANICKED; AND ALLOWED THAT TO CLOUD HER RESPONSE.