Pictured above is the Western Electric 6B 1,000 watt AM transmitter with the companion speech input bay on the right. The transmitter consists of two bays, an exciter unit on the left, and the power amplifier unit on the right. The round speaker on the table is the Western Electric 540-CW Loud-Speaking Telephone monitor speaker.
Shown above is the exciter compartment of the left bay with the access door open. In the foreground on the right is the crystal oscillator unit, a model 700C which was the standard crystal oscillator unit used in the following generation of Western Electric transmitters – quite possibly an update from the original crystal oscillator. It was standard practice to use two 700 Oscillators, one as the primary, the other as a hot-standby (note that the standby unit is missing). On the rear deck are two stages of RF amplification employing two type 242C triodes. Crystal oscillator unit selection and RF amplification stage tuning controls are located directly under the tube access door.
The model 700 Oscillator unit contains the crystal (610kHz) installed in a thermostatically controlled oven. It was necessary to regulate the temperature of the crystal in order to comply with government frequency stability regulations. The oscillator tube is a Western Electric type 71A.
Above is the Power Amplifier compartment in the right-hand bay. It contains a 276 tube on the left, two type 212E triodes and a type 328 water-cooled final amplifier tube. Western Electric used grid modulation in their broadcast transmitters up to 5,000 watts during the 1920's and 30's. The levers in front of the 212E tubes control the water flow to the final amplifier tube (Inlet ON-OFF). A radiator fan and circulating pump were located externally.
From left to right: 276C, 212E (2), and the 328A water-cooled final amplifier which runs 1000 watts.
Below the tube access door are the 3rd Amplifier, Antenna Tuning, and Power Amplifier Tuning controls (top row of 3 “steering wheel” controls). The bottom row controls the three motor-generators used to supply 24VDC (filaments), 250VDC (grids) and 4000VDC (plate). The motor-generator sets were normally located in a separate room.
Access to the additional tuning controls and coarse frequency adjustment was made from the rear of the transmitter. Two locking screened doors are provided for safety.
The current goal at K6GLH is to fully restore this transmitter and relocate it to the 160 meter ham band; probably on 1925 KHz. While this is an ambitious project, this is a classic specimen of California Broadcast Radio Americana that needs to be preserved and celebrated. Check back occasionally for updates and progress reports on this noble project.
Content and photographs courtesy of K6GLH and the K6GLH collection.
