Development of a prototype high temperature amplifier for geothermal well logging. Final report

A high temperature amplifier for use in geothermal well logging was developed. This development was based on the use of ceramic vacuum tubes as the active circuit element, since these tubes have the capability to operate in the high ambient temperature environment. The primary goal of this program was to design, build, and deliver a prototype amplifier capable of continuous operation in a 250/sup 0/C environment. A development program designed to meet this goal covered four phases. These phases were (1) development of the basic circuit configuration with conventional, low cost glass envelope vacuum tubes; (2) modification of the circuitry to accommodate the ceramic vacuum tubes; (3) a 1000-hour duration temperature cycle (48 hours at 260/sup 0/C and 2 hours at 20/sup 0/C); and (4) development of a prototype, deliverable amplifier. The following sections discuss the high temperature amplifier development program. Section 2 describes the amplifier performance, including design requirements, circuit design, development program, and the prototype amplifier. Section 3 presents test results from two breadboard models, one with conventional glass tubes and one with ceramic tubes, and the prototype amplifier. Section 4 describes the operation of the prototype amplifier. Circuit equations used for analysis and tube characteristics are contained in the appendices