SMA PLT HAD STUCK MIKE AND DISCOVERED NO XPONDER IN THE ACFT. HE HAD FILED AN IFR FLT PLAN.

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I COMPLETED A STANDARD PREFLT ON A CESSNA C150 WITH A 180 HP ENG. THE INST PANEL WAS COVERED WITH A NEW SECURITY SHIELD OVER THE AVIONICS WHICH I REMOVED DURING THE PREFLT. AFTER ENG START; CONTACTS WITH ATIS; CLRNC DELIVERY; AND GND CTL WERE NORMAL. A CLRNC WAS READ BACK CORRECTLY IN THE RUN-UP AREA AND IT WAS THEN THAT I REALIZED THE XPONDER WAS MISSING. WE PREVIOUSLY HAD THE DME OUT OF THE AIRPLANE FOR REPAIRS SO THE EMPTY SLOT DIDN'T LOOK UNUSUAL. AFTER I WENT THROUGH AN EMOTIONAL VERBIAGE OF DISGUST ON WHAT I THOUGHT WAS THE INTERCOM; GND CTL ADVISED ME THAT I HAD A STUCK MIKE. AFTER AN APOLOGY TO THE TWR FOLKS; I FOUND THE SOURCE OF THAT PROB WHICH WAS THE PUSH TO TALK SWITCH ON THE YOKE. NEXT I ASKED THE TWR IF I COULD GO IFR WITHOUT THE XPONDER AND THEY SAID THEY WERE TRYING TO COORDINATE IT. THE REPLY FROM APCH WAS THAT I COULDN'T GO IFR IN THE CLASS B WITHOUT A XPONDER (THAT MADE SENSE AND RELIEVED ME OF THE MENTAL BURDEN OF HAVING FILED AN EQUIP CODE AS A SLANT A WITH XPONDER). THE TWR SAID I WOULD HAVE TO REMAIN CLR OF THE CLASS B AIRSPACE. THE TWR ASKED IF I WANTED A DOWNWIND DEP (IT WAS VFR) AND I ACCEPTED. WE TOOK OFF VFR AND STAYED CLR OF THE CLASS B AIRSPACE. UNABLE TO EVEN SQUAWK 1200; I WAS GRATEFUL FOR THE VFR DEP. MY FIRST PROB WAS NOT REALIZING THE XPONDER WAS MISSING DURING PREFLT. INTERESTINGLY; THE PREFLT WAS NOT RUSHED. IT WAS PRETTY COMPLETE BUT COMPLICATED BY THE NEW NON-STANDARD SECURITY PANEL AND BY ME BEING USED TO A 'HOLE' IN THE PANEL WHEN THE DME WAS BEING REPAIRED. THE SECOND PROB WAS THE STUCK MIKE (MECHANICAL). THE THIRD PROB WAS HAVING TO FLY WITHIN THE 30 MI VEIL WITHOUT MODE C EVEN THOUGH COORDINATED WITH ATC. APCH CTL DOESN'T NEED ANY ADDITIONAL CHALLENGES EVEN WHEN THERE IS LITTLE TFC. ALL THIS COULD HAVE BEEN PREVENTED. A BETTER PREFLT BEFORE ENG START WOULD HAVE RECOGNIZED THE XPONDER PROB. SEEING THE SMALL 'T' ON THE RADIO MIGHT HAVE MADE ME REALIZE THE PUSH TO TALK BUTTON WAS STUCK.