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Amp switches     Why Two Switches?

 

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

Proper use of the Power and Standby switches might help you prolong the life of your tubes.  You just have to follow two rules.

 

THE RULES

 

  1. Before turning the Power switch on, make sure the amp is in Standby mode.  Give the amp several minutes to warm up before you switch it out of standby.

  2. If you want to silence your amp without turning it off, for example to take a break, then switch the amp to standby but not for more than 15 to 20 minutes.


That's all there is to it.  When you shut down the amp, you can just flip the power switch off or you can switch to standby too so it's set correctly the next time you warm up your amp.

 

THE WARM-UP

 

Every vacuum tube has at least two metal electrodes.   They all have a "cathode" and an "anode".

The cathode is heated to a very high temperature so that electrons, which are quite speedy to begin with, gain enough extra energy to break away from the cathode's alkaline earth metal oxide coated surface.

This "thermionic" emission begins as the cathode starts to glow red.  When everthing is hot, a cloud of electrons (negative charge) forms in the vacuum surrounding the cathode and the tube is ready to go to work.

A high positive charge, often called the B+, is then applied to the anode or "plate" of the tube.  The plate attracts and collects the free electrons which are then put to work powering your speakers before they complete their circuit.

 

THE REASON FOR RULE #1

 

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

The Standby switch was invented to disconnect the B+ from the plates for just this reason.  It lets you prevent cathode stripping by allowing the tubes to reach full operating temperature before you connect the B+.

 

THE REASON FOR RULE #2

 

Conversely, if a cathode is hot for extended periods with no B+ to draw current, a destructive process called cathode poisoning occurs.  The old-timers called this sleeping sickness.

Without current, a high resistance layer builds up between the metallic cathode and its oxide coating.  This unwanted resistance can easily increase the noise, and also decrease the gain, of the vacuum tube.

 





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