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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 could help you prolong the life and sound quality of your tubes.  Just follow two simple rules.

 

THE RULES

 

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

  2. If you want to quiet your amp during a break without cooling it off, switch to Standby mode but not for more than 15 to 20 minutes.

That's all there is to it—switch the power off regardless of the standby mode.

 

THE WARM UP

 

Every vacuum tube has at least two conducting terminals called the "cathode" and the "anode".

In action, the cathode is heated to such a high temperature that electrons, which are speedy to begin with, gain enough additional energy to break away from the cathode's alkaline earth metal oxide coated surface.

This thermionic emission begins as the cathode begins to glow red.  Eventually, a cloud of electrons (negative charge) builds up in the vacuum surrounding the cathode.  At this point, the tube is ready to go to work.

To open the valve, a high positive charge often called the B+, is applied to the tube's anode, also called the plate.  The plate attracts and collects the free electrons, which are put to work powering your speakers before completing their circuit.

 

CATHODE STRIPPING—THE REASON FOR RULE "A"

 

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 surrounding electron cloud.  The resulting damage to the cathode's coating is called cathode stripping.

The Standby switch was invented to withhold the B+ from the tube plates for just this reason.  You can prevent cathode stripping by letting your tubes reach full operating temperature before applying the pressure.

 

CATHODE POISONING—THE REASON FOR RULE "B"

 

Conversely, if a cathode is left hot for extended periods with no plate voltage to collect the emitted electrons, a destructive process called cathode poisoning occurs.  The old-timers called this sleeping sickness.

Without current flow, a high resistance layer builds up between the cathode's metal base and its oxide coating.  This unwanted resistance decreases the gain and also increases the noise of the vacuum tube.

 





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