The Clough Brengle model OC RF Signal Generator, appears to be the first signal generator offered by the company. Introduced sometime in 1934 or 1935, this oscillator proved to be one of the most popular of all the equipment Clough Brengle produced. The example pictured on this page is serial number 4999, which indicates at least several thousand copies were made.
A copy of the schematic can be seen here.