I checked my Ampeg manual and I’ll continue to use mine , here’s what it says,
STANDBYSWITCH:Pressthetopof the switch to turn the Standby mode on. The Standby mode allows the tubes to warm, or remain warm, without high voltage being applied to them, which helps to extend tube life. This switch should be OFF when first turning the amplifier on. Allow the unit to warm up for at least 60 seconds before switching the Standby to the ON position. During short periods of non-use, the amp should be put into Standby mode.