Amplifier C class

It's still in class B class c starts when modulating signall is at least 10% of peak halfcycle voltage higher from zero line. For example if we have sine signal with +-20v peak/peak voltage class c begin when transistors starts work no earlier than signall voltage reach +-2v. There is a other way that states class C begins when transistors are turn on at least when signall is at 20% higher of their turn on voltage so for typical transistor a 20% higher than 0.7 V. But those are details and differs a little in various places but rule is one a c class must delay turn on. Simple method is to install a diode in series with base to increase turn on voltage by 0.7 from diode voltage drop or bias base below emitter by 0.5 or 0.7 volt so for typica turn on u muet add a drop voltage o it delay turn on. Base bias in reverse not recomended unles u are sure that transistor can handle such when adds to this various tranients. This reverse base handling in bjt is very limited. Some models break at emitter base back voltage as low as 3 volts so when some transient adds a zener back breakover happens and if this breakover current will not be limited it will destroy device. Ofcourse if this current is limited it's not harmfull at all but installing a resistor with base is not possible when forward base curent expected will be great and if u install blocking diode u have a class c just from diode drop so no bias is need.