Push–pull output: Difference between revisions

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=== Push–pull tube (valve) output stages ===

{{See also|Valve audio amplifier – technical#The push–pull power amplifier}}

[[Vacuum tube]]s (valves) are not available in complementary types (as are pnpPNP/npnNPN transistors), so the tube push–pull amplifier has a pair of identical output tubes or groups of tubes with the [[control grid]]s driven in antiphase. These tubes drive current through the two halves of the primary winding of a center-tapped output transformer. Signal currents add, while the distortion signals due to the non-linear [[Current–voltage characteristic|characteristic curve]]s of the tubes subtract. These amplifiers were first designed long before the development of solid-state electronic devices; they are still in use by both [[audiophile]]s and musicians who consider them to sound better.

Vacuum tube push–pull amplifiers usually use an output transformer, although [[Output transformerless|Output-transformerless (OTL)]] tube stages exist (such as the SEPP/SRPP and the White Cathode Follower below).{{citation needed|date=December 2012}} The phase-splitter stage is usually another vacuum tube but a transformer with a center-tapped secondary winding was occasionally used in some designs. Because these are essentially square-law devices, the comments regarding [[Distortion#Cancellation of even-order harmonic distortion|distortion cancellation]] mentioned [[Push–pull output#Square-law push–pull|above]] apply to most push–pull tube designs when operated in [[Power amplifier classes#Class A|class A]] (i.e. neither device is driven to its non-conducting state).