An RF final amplifier for a shortwave amateur radio transmitter from a 1938 radio magazine. Called the "10-20", sold by Radio-Television Supply Co. of Los Angeles, it could deliver 1 kilowatt continuous wave or 600 watts amplitude modulation on the 10 or 20 meter band (15 or 30 MHz) using two type 100TH triode vacuum tubes. The two triodes were operated in push-pull, driving the resonant tank circuit visible at right consisting of two parallel plate capacitors connected to the air core inductor. It came with 4 plug-in coils to cover the two bands, and sold for $32.50 in kit form without tubes, and $37.50 wired.