gq: Leakage is equivalent to a resistor in parallel with the capacitor. Constant exposure to heat can cause dielectric breakdown and excessive leakage, a problem often seen in older vacuum tube circuits, particularly where oiled paper and foil capacitors were used. In many vacuum tube circuits, interstage coupling capacitors are used to conduct a varying signal from the plate of one tube to the grid circuit of the next stage. A leaky capacitor can cause the grid circuit voltage to be raised from its normal bias setting, causing excessive current or signal distortion in the downstream tube. In power amplifiers this can cause the plates to glow red, or current limiting resistors to overheat, even fail. Similar considerations apply to component fabricated solid-state (transistor) amplifiers, but owing to lower heat production and the use of modern polyester dielectric barriers this once-common problem has become relatively rare.
Question: With what value is a resistor in parallel with a capacitor equal to? Question: What can cause excessive leakage in a capacitor? Question: What sort of capacitors are used to carry a varying signal from the conductive plate of one tube to the grid circuit of the next stage? Question: What type of capacitor can cause signal distortion in the downstream tube? Question: If the grid circuit voltage is increased beyond its regular bias setting, what can happen to the conductive plates in power amplifiers?