UNAUTH PENETRATION OF CLASS B AIRSPACE BY C-150. TRAINING IN PROGRESS.

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WHILE CLBING OUT ON DUAL XCOUNTRY; CALLED DEN APCH TO GET RA AND CLRNC INTO CLASS B AIRSPACE. UPON ESTABLISHING CONTACT WITH DEN APCH; HE INFORMED US WE WERE ALREADY IN CLASS B AIRSPACE. BECAUSE OF CLASS B AIRSPACE TIER IS 7000 FT MSL IN THIS AREA. OUR XPONDER ENCODER SHOWED US AT 7400 FT MSL. OUR ALTIMETER (WITH PROPER SETTING) SHOWED US AT 7000 FT MSL. WE INFORMED DEN APCH OF THIS DISCREPANCY AND STOPPED OUR ALT SQUAWK. APCH GAVE US CLRNC INTO CLASS B AIRSPACE TO CLB TO OUR CRUISING ALT OF 7500 FT MSL. I WAS INSTRUCTING A STUDENT ON HIS FIRST DUAL XCOUNTRY AND FELT HIS WAS NOT THE PROPER WAY TO INTRODUCE HIM TO CLASS B AIRSPACE. THE MECHANICAL CONDITION OF THIS OLD CESSNA 152 AND ITS INSTS WERE A FACTOR. IT IS INDEED SAD THAT CESSNA CANNOT MAKE NEW SINGLE ENG ACFT. THOSE OF US INVOLVED IN GA WILL CONTINUE TO HAVE TO 'MAKE DO' WITH OUR OLD ACFT AND EQUIP. I HOPE STUDENTS SOME DAY WILL BE ABLE TO ENJOY A SPARKLING NEW ACFT LIKE I WAS ABLE TO WHEN I WAS A STUDENT. EVEN THOUGH WE DID NOT VIOLATE CLASS B AIRSPACE; ATC THINKS WE MAY HAVE SO THAT IS WHY I FILED THE RPT.