In a grounded grid amplifier using a triode vacuum tube, the plate is connected to the pi-network through a:

In a grounded grid amplifier, the plate (anode) operates at a very high DC voltage. To safely transfer the amplified radio frequency (RF) signal to the pi-network (and subsequently the antenna), a capacitor is placed in series between the plate and the pi-network. This component is called a DC blocking capacitor. Its primary job is to allow the alternating current (AC) RF signal to pass through while completely blocking the dangerously high DC voltage from reaching the tuning circuits and the antenna system. Other capacitor types are incorrect for this specific role. By-pass capacitors are used to shunt RF to ground, tuning capacitors are variable components used to adjust resonant frequencies, and electrolytic capacitors are polarized components completely unsuitable for passing high-power RF signals.