As soon as the same may be legally paid under the Constitution of Nebraska, each judge of the district court and each judge of a separate juvenile court shall be paid a salary of thirty-nine thousand five hundred dollars per annum. On January 8, 1981, the salary shall be increased to an amount equal to six percent over the base salary. For the purposes of this section base salary shall mean the amount derived by increasing thirty-nine thousand five hundred dollars by six percent. On January 6, 1983, and thereafter the salary paid shall be an amount equal to ninety-two and one-half percent of the salary set for the Chief Justice and judges of the Supreme Court. Such salary shall be payable in equal installments.