The schematic diagram shows a typical TRF receiver. This particular example uses six triodes. It has two radio frequency amplifier stages, one grid-leak detector/amplifier and three class ‘A’ audio amplifier stages. There are 3 tuned circuits "T1-C1, T2-C2, and T3-C3". The second and third tuning capacitors, "C2" and "C3", are ganged together "(indicated by line linking them)" and controlled by a single knob, to simplify tuning. Generally, two or three RF amplifiers were required to filter and amplify the received signal enough for good reception.