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Tube Amplifiers

 

Tube amplifiers are the preferred type of amplifiers for most musicians.  However, the price, weight and maintenance needed usually deters many.   These amplifiers are expensive (usually $700 to $2,000), and there weight can be very significant (50lbs - 82lbs, or 20kg - 35kg). 

However, the sound of these amplifiers are very coveted for most of us.  For the average bassist, the Ampeg SVT is the holy grail of tube amplifiers (sometimes known as valve type).  The reason for the great sound is number of triode stages and final output power section (a parallel push-pull final stage). Each amplifier section slightly equalizes the sound of the instrument, by boosting the highs and mids of bass, essentially performing a mild signal processing on the bass.  The amplifier uses 12AX7's, 12AT7's, and 12AU7's in the input pre-amplifier section.  There are four pairs of triode amplification, which is eight pre-amps chained together.   This finally drives a six pair set of power amplifier tubes (either 6146B's or 6550's depending on which year the unit was designed).  The driver section is push-pull amplifier stage which then drives a quad tube set of push-pull in parallel set.  The result is a power amplifier operating in a class AB condition, and driving a large audio transformer for 300 watts of clean power.  The sound of the bass goes through eleven tube amplifier stages in the process.  This is the main reason for the great sound of this amplifier.  Having played through a couple of these amps in the past I can attest to how great the sound is.  Also, it should be remembered that the amplifier is usually coupled with eight 10 inch speakers.  The cabinet is really four cabinets with two 10 inch woofers in each box.  These are in an infinite baffle design, which results a very tight and clean sound.  The speaker surface area is equivalent to two 20 inch woofers.  A nice wall of sound for most needs.

The Ampeg SVT Classic sold today is has the same basic tube preamplifier section, but uses MOSFET's (a type of solid state transistors) for the final output section.  This yields an output of 450 watts.  MOSFET's do have a capacitive property and colors the sound some what like a tube does, but not as much as tubes will.  However, most of the sound like quality is still present in this amplifier.

The highest wattage amp, that I am aware of, is the Trace Elliot all tube amplifier, at 400 watts. 

 

Check the Resources page for locations to purchase tube amplifiers.

 

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