- Most 'RAT' Amps use the 'Twin-Rectifier' System -
The Mains 'On/Off' Power Switch has 3 Positions.
'Centre' Position is AMP OFF.
'Back' Position is AMP ON, using the Valve Rectifier.
'Forward' Position is AMP ON using the Silicon Rectifier.
The Only Reason for Fitting a Valve Rectifier in a Modern Amp is to Induce Vintage Style 'SAG'. The Amp does not require a 'Standby' Switch as long as it is Switched 'ON' to the Valve Rectifier Position.
All Amplifiers use a Rectifier to convert the Raw AC Voltage from the Mains Transformer into DC Voltage. The Amp Circuits Need DC Voltage to work. If, for example, you Hit a Power Chord on your Guitar, the Amplifier Circuitry Suddenly Demands a Large Dose of Power from the Mains Transformer. Silicon Diodes are Extremely Efficient and can convert the Raw AC into DC almost instantaneously, to Feed the Amplifiers Needs. Valve Rectifiers are a Different Story. Generally Speaking, they can't Cope with Sudden High Demands of Energy and they 'Starve' the Amp of Power until they can catch up with the Demand - This is Called 'SAG' - and it Sounds GREAT!
The typical sound Produced by an Amp using a 'Silicon' Rectifier would be -
- Attack - Sustain - Release - Decay -
Using a 'Valve' Rectifier, the Sound will be Closer to -
- Attack - Swell - Extended Sustain - Release - Decay -
To your Ears -
In 'Silicon Rectifier' Mode the Initial Note Attack is Sharp and Crisp - Like a Modern Amp.
In 'Valve Rectifier' Mode the Initial Note Attack is almost Soft and Laid-Back with Longer Sustain - Like a Vintage Amp.
It is OK to Switch Between Rectifiers While the Amp is Running.
This System works equally well with 'Class A' - 'Class A/B' - 'Single Ended' - 'Push Pull' - 'Cathode Bias' and 'Fixed Bias' Amp Designs.
Note - The main function of a 'Standby' Switch is to Allow the Valve 'Heaters' to warm-up before the High Voltage Hits the Amplifier Valves. Using a Valve Rectifier the High Voltage is delayed (to the rest of the Amp) as the Valve Rectifier warms-up. A 'Standby' Switch can still be fitted, and used, but it is not a requirement when using a Valve Rectifier.