Solid State Rectifier for 5AR4, 5U4, 5Y3 Tubes Solid State Rectifier Direct plug-in replacement for 5AR4, 5U4 and 5Y3 rectifier tubes in amplifiers with center tapped secondary power transformer. Use when less 'sag' is desired in the power supply; just switch back to the tube rectifier when 'sag' is desired. NOTE! Because there is no warm up of a rectifier tube when using this solid state device, it is critical that a standby switch is used that will allow the power tube filaments to warm up and generate an electron 'cloud' around This will prevent 'cathode stripping' in the power tubes It is a good idea to use a standby switch when using vacuum tube rectification, but it is critical when using solid state rectification.