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Amp switches     Why Standby?


If your guitar amp has both a Power switch and a Standby switch, then it uses vacuum tubes (valves).  It will take a while for the amp to warm up before making sound.

Proper use of the Power and Standby switches could help you prolong the life and the sound quality of your tubes.  Just follow two simple rules.




  1. Before turning the Power switch to On, make sure the amp is in Standby mode.  Allow the tubes to warm up for several minutes before you switch the amp out of Standby mode.

  2. To quiet your amp during a break without cooling it down, switch the amp to Standby mode.  But don't leave it in Standby for more than 15 to 20 minutes.

It's just that simple and here's why...




Every vacuum tube has at least two terminals for conducting electrons.  The "cathode" emits electrons and the "anode" collects them.

The cathode is heated to such a high temperature that electrons in its coating (often an alkaline earth-metal oxide) gain enough energy to break away from the coating.

This "thermionic emission" creates a red glow.  Eventually, a cloud of electrons (negative charge) builds up in the space around the cathode.  The tube is then standing by, ready to go to work.

When you switch the amp out of Standby mode, you are connecting a positive voltage (often called B+) to the tube's anode, or "plate".

The positively charged plate attracts the emitted electrons and uses the electric current to power your speakers, etc.  Electrons continue to move into the cathode's oxide coating, maintaining its emission.




If B+ is applied to a tube's plate before its cathode is red hot, electrons will be ripped from the cathode's oxide coating instead of being drawn from the surrounding electron cloud.  The resulting damage to the coating is called "cathode stripping".

The Standby switch was invented to withhold the B+ from the plates until the tubes are warmed up.  You can reduce cathode stripping by letting the tubes reach their operating temperature before you put them to work.




Conversely, if a cathode is red hot for long periods without a B+ to collect the electrons, a destructive process called "cathode poisoning" occurs.  The old-timers called this "sleeping sickness".

Without flowing electrons, a high resistance layer builds up between the cathode's metal base and its oxide coating.  This resistance decreases the gain and increases the noise of the tube.  To fight cathode poisoning, use the Standby mode judiciously.


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