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Heritage B-15 Bass Amplifier
Heritage B-15 Bass Amplifier Heritage B-15 Bass Amplifier
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A brief history of the tube:
In 1883, Thomas Edison discovered that electrons would flow from a suspended filament when enclosed
in an evacuated lamp. Years later, in 1905, John Ambrose Fleming expanded on Edison’s discovery and
createdthe“FlemingValve”.Then,in1907,Dr.LeedeForestaddedathirdcomponent–thegrid–to
“Fleming’sValve”andthevacuumtubewasafactoflife.Thedoortoelectronicamplificationwasnow
open.
During World War II, data gleaned from their intensive research on the detectors used in radar systems
led Bell Telephone Laboratories to the invention of the transistor. This reliable little device gained quick
support as the new component for amplification. The death of the vacuum tube seemed imminent as
designers, scientists, and engineers reveled in the idea of replacing large, fragile glass tubes with these
small, solid-state devices.
However, there were (and still are) many serious listeners who realized that the sound produced by a
“transistor” amplifier is significantly different from that produced by a tube amplifier with identical design
specifications. They considered the sound produced by these new solid-state devices to be hard, brittle,
and lifeless. It was determined that solid-state devices produced a less musical set of harmonics than
tubes. When pushed past their limits, they tend to mute the tone and emphasize the distortion.
Tubes, on the other hand, produce a more musical set of harmonics, the intensity of which may be
controlled by the player. This characteristic adds warmth and definition to the sound which has become
the hallmark of tube amplifiers. When tubes are driven into clipping, the harmonic overtones can be both
sweet and pleasing or intense and penetrating, depending on the musician’s taste and playing technique.
Over the years, application engineers have designed a number of outstanding solid-state amplifiers that
sound very, very good. Some use special circuitry which enables them to simulate distortion
characteristics of a tube amplifier. However, the tube amplifier, still held in the highest esteem by many
musicians, offers a classic “vintage” sound in a contemporary market.
Tube types and usage:
The Ampeg Heritage B-15 contains three types of tubes: preamplifier tubes, power tubes and a rectifier
tube.
Preamplifier tubes
amplify the signal from the instrument and shape the sound. They are inherently
microphonic (mechanically pick up and transmit external noises). Since these tubes are used in the critical
first stages of a tube amplifier’s circuitry, it is very important that any replacements are high-quality, low
noise/low microphonic tubes for this application. Although tubes of this quality may be difficult to find and
typically cost more than “off-the-shelf” tubes, the improvement in performance is worth the investment.
The preamplifier tubes in the Ampeg Heritage B-15 are three 6SL7 (N.O.S. JAN Philips ECG 6188).
These tubes use larger, octal, sockets and are physically larger than most typical preamp tubes
(12AX7 / 12AT7 / 12AU7 / ECC81 / ECC82 / ECC83 / 7025). The Ampeg Heritage team chose 6SL7
tubes for period authenticity, as these tubes came standard with the 1964 Ampeg B-15NC and 1966
Ampeg B-15NF. Nothing sounds closer to the real thing than the real thing and to ensure the best
possible sound out of the Heritage Ampeg B-15, we sourced the N.O.S. (New Old Stock) JAN (Joint Army/
Navy) Philips ECG 6188 that is a Super Military 6SL7. The 6SL7 preamplifier tube closest to the power
tubes is used to drive the power tubes. It is possible to change the sound of the amplifier by changing
the type of preamp and/or driver tubes. When making any modification to your equipment, it is highly
recommended that you consult with a qualified service center.
Important information about tubes