In this letter, Glenn Joseph reports that the vacuum-tube amplifier in the early Beckman pH meter model is (still) not functioning properly. One of the fixes he proposes is replacing the vacuum tubes with a glass electrode system, which is what ultimately happened.

Arnold Beckman invented his first pH meter in 1934 at the request of a chemist from the California citrus industry, who needed an accurate way to measure the acidity of his product. The resulting instrument kicked off rapid development not only of Beckman Instruments, Inc. but also of the electronic scientific instrument industry.