RADIO COM PROBLEM CAUSES FLC ON ACR MLG TO CREATE PROBLEM FOR TWR CTLR IN BEING UNABLE TO ESTABLISH RADIO CONTACT WITH MLG.

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INITIAL TAXI CLRNC FROM GND CTL (121.9) WAS TO TAXI TO RWY 19 VIA RWY 6/24. APCHING THE DEP END OF RWY 19 ON THE PARALLEL TAXIWAY WE CHANGED TO TWR (119.5). WE WATCHED 1 AIRPLANE LAND AS WE HELD SHORT OF RWY 19 AND THEN WATCHED ANOTHER LINE UP ON FINAL. AT THIS POINT WE REALIZED WE WERE NOT HEARING ANY RADIO TRANSMISSIONS AND RECHKED OUR RADIOS. THE CORRECT FREQ (119.5) WAS SELECTED BUT THE VOLUME WAS TURNED DOWN. WHEN WE ADJUSTED THE VOLUME BACK TO NORMAL WE HEARD TWR GIVING THE ACR FLT ON SHORT FINAL MISSED APCH INSTRUCTIONS. AFTER TWR ISSUED THE MISSED APCH INSTRUCTIONS THEY ASKED US IF WE WERE ON FREQ. WE ACKNOWLEDGED TWR AND TOLD THEM WE WERE HOLDING SHORT OF RWY 19; OUR LAST CLRNC. TWR THEN TOLD US THAT THEY HAD CLRED US ONTO RWY 19 TO HOLD. WE HAD NOT ACKNOWLEDGED ANY RADIO CALLS FROM TWR AND SINCE THEY COULD NOT TELL IF WE WERE ON THE RWY OR NOT; THEY SENT THE ACR FLT AROUND. TWR THEN ASKED US IF WE HAD HAD ANY RADIO PROBLEMS AND WE ACKNOWLEDGED THAT WE HAD. AT THIS POINT TWR CLRED US ONTO THE RWY AND CLRED US FOR DEP. THE SUBSEQUENT FLT WAS NORMAL. THE AIRPLANE THAT WE WERE FLYING IS ONE OF A HANDFUL OF MLGS THAT IS NOT STANDARDIZED WITH THE REST OF THE FLEET. THIS PARTICULAR ACFT HAS A SINGLE VOLUME CTL KNOB FOR THE COM RADIOS WHEREAS MOST OF THE MLGS HAVE INDIVIDUAL AUDIO PANEL CTLS FOR EACH PLT. THE LIKELIHOOD OF THE RADIO VOLUME BEING TURNED DOWN TOO LOW IS VERY MINIMAL ON THE NORMAL MLG. HOWEVER; THE SINGLE VOLUME CTL KNOB RADIO LENDS ITSELF TO INADVERTENTLY BEING TURNED DOWN TOO LOW. WE HAD IT HAPPEN TO US SEVERAL TIMES DURING THE 2 FLTS WE HAD WITH THIS PARTICULAR ACFT.