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
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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