At left, A. H. Saxton, NBC Western Division Engineer, explains the workings of one of the KPO transmitter tubes to Alice Tyler of the NBC Plant Department.  This tube was kept on display at the NBC studios at 111 Sutter Street .  At right, he gives the same demonstration to NBC singer Helen Musselman in front of the big transmitter.. 

The water cooled final amplifier tubes were rated for 100 KW, and cost about $2,000 each in 1933!