KPO 50kW Transmitter Building
Belmont, California


The KPO transmitter building was built under contract to NBC by General Electric in 1932, along with the transmitter itself.

First Floor: In the main room were located the filament and bias motor generator sets, their associated switching and starting equipment, and the battery charging generator and control panel. Other rooms included the main building power service, filament circuit filter reactors, the battery reactor, intermediate rectifier plate transformer, final amplifier plate transformer, voltage rectifier, rectifier filter reactor, water cooling equipment, and the batteries which provided the plate and filament supplies for the tubes of the audio equipment. Also on the first floor were a kitchen, garage, and spare parts storage.

Second Floor: The main room contained the transmitter itself, along with the transmitter operator’s desk. Another room contained the speech amplifier rack and remote control equipment. Also on the second floor were the engineer’s living quarters, office, shop and storage room.

Outdoors: At the rear of the building was a large concrete pedestal which held the primary three phase AC service transformers and the giant radiator blower, which was the primary cooling system for the distilled water that cooled the transmitter tubes. A water spray pond provided backup cooling, and its water was used to cool the heated distilled water through a heat exchanger.

Two engineers were required on duty at all times to operate the transmitter. One engineer watched the transmitter, while the other engineer manned the speech amplifier equipment and adjusted the audio level for proper modulation of the transmitter. These engineers were also occupied with a busy schedule of maintenance.

This building continues in use today as the transmitter site for KNBR, today’s descendant of KPO.

Voices Out Of The Fog

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All articles copyright © 1997-2006 by John F. Schneider. All rights reserved.
Reprinted with the generous permission of the author.

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