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An Introduction to Compression: Basic Compression - A free download from Audio Masterclass

An Introduction to Equalization - A free download from Audio Masterclass

Equipping Your Home Recording Studio - A free download from Audio Masterclass

What is production? Part 3: Recording

Fixing a problem note with Auto-Tune

Do you need more plug-ins? Or more skills?

Setting the gain control on your audio interface for recording

A brief introduction to acoustic treatment

Do some microphones respond to EQ better than others?

The new Apple HomePod smart speaker - what difference will it make to your mixing and mastering?

Why your new monitors should make your mix sound bad

How to set a graphic equalizer

The importance of managing configurations and preferences in professional work

Why is there a silvery coating inside a vacuum tube?

Have you ever wondered why there is a silvery patch inside a vacuum tube? Is it there for a purpose? Does it affect the sound of the tube?

A studio isn't a proper studio without at least one vacuum tube device. The sound quality of tubes is unique and hard to emulate digitally (and impossible to emulate using transistor circuitry).

You may have wondered however why most tubes have a silvery coating on the inside. This is usually quite easily visible. Just look in the back of your guitar amp.

Tubes work by controlling the flow of electrons through a vacuum. It has to be a vacuum because otherwise the air molecules would get in the way. That's why they are called vacuum tubes :-)

But creating a 'hard' enough vacuum inside a glass envelope is quite difficult. So the trick is to pump out as much air as possible, seal the tube, and then absorb what air is left in some way.

Absorbing as much as possible of the last remnants of air inside is the function of the 'getter'.

The getter is a small cup inside the tube containing a strongly reactive metal, such as barium. When the tube is pumped out and sealed, the getter is fired, producing a 'getter flash' inside the tube.

The silvery patch that is visible is created by the getter. The getter has performed its function by absorbing much of the remaining oxygen.

And the harder the vacuum, the better the performance of the tube. Sometimes the getter flash might be uneven in appearance, but that doesn't make any difference to the sound or how well the tube works. If it turns white however, that's a sign that that air is leaking into the tube. Time for a replacement I think.

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By David Mellor Thursday February 10, 2011
Learn music production