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Saturday, September 22, 2012


Most people don't use the standby switch on their amp correctly, at least in the way that I understand things. I wonder why these are still being put on amps. Yes, I understand the reasoning, but I haven't really seen tubes wearing out that much faster. Maybe it's a subtle difference.

The idea behind a standby switch is to give the tube heaters a chance to warm up to operating temperature before you apply the B+ voltage and the tube starts working. Failure to do so leads to cathode stripping (whatever that is), and is detrimental to tube life. What I've read, and believe enough to follow myself, is you should
  1. turn on the power switch
  2. wait at least 30-60 seconds
  3. turn on the standby switch, and make noise.
Powering down is the opposite:
  1. turn off the standby switch,
  2. wait at least 30-60 seconds,
  3. turn off the power switch
But where most people go wrong is the time in between those two events. At the end of the first set, don't use the standby switch. Leave the amp on. Unplug your guitar or turn the volume down at the end of a set, but leave the amp on the whole night. Component failures are most likely to happen at start up--caps are uncharged and there's a large current surge, things are cold and need to heat up, etc. Think about a light bulb. How many times have you seen one fail when it's been on a while? Most fail when you turn them on.

Leaving your amp on the whole night is easier on the amp because there's only one startup. After everything is warmed up and ready to go, it coasts along until the end of the night. If you're turning it off because it's getting warm and you don't want to cook the components, consider installing a small fan. Even a little air movement will help immensely. I've installed fans in my Fender amps because I don't like the idea of the downward hanging tubes cooking the components in the chassis above them. I think this is a drawback for combo amps, but then it can't be too big a deal because there are so many combo amps doing just fine. If you what to install one, you can run a 12 volt fan off the 6.3 volt heater supply. Sometimes you can hook it up directly, while other times you may need to add a diode and capacitor to give it a DC voltage. It will run slower than it was designed to, but if you can feel any air movement, it will move the heat out. Running it slower has the benefit of making it quieter.

If heat is a concern, you may have bigger problems. The tubes will get hot enough to burn you, but nothing else should be so hot that you can't touch it for a few seconds. Especially watch the transformers, as they are the most expensive items in the amp. Heat means too much current is being drawn, and you need to find out why. Sometimes it's as simple as a bias adjustment, other times it might be rusty laminations in the transformers causing eddy currents and robbing power.

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