The county treasurer, upon order of the commissioners and with the approval of the county convention as required in N.H. Rev. Stat. § 29:8, may incur debt in anticipation of the receipt of taxes for the financial year in which the debt is incurred. Such funds may be used to pay maintenance and operating expenses incurred during the current financial year. In this section, maintenance and operating expenses shall include all appropriations approved by the county convention for the current financial year. Tax anticipation notes may be issued therefor to an aggregate principal amount not exceeding 80 percent of the total appropriations approved by the county convention for the preceding financial year. All notes issued under the authority of this section shall be general obligation and shall be payable not later than the final day of the applicable budget year.