Five Classic Amps

A Tone-Spotter’s Arsenal To Cover It All

Five Classic Amps
(LEFT) A 1958 Fender 5F4 Super Amp and a 1964 Vox AC30/6 “Top Boost” Vox AC30/6: Jim Elyea/Vox Amplifiers: The JMI Years.
When it comes to classic guitar tones – whether it’s blues through a Dumble, country through a Fender, rock through a Marshall, or jazz through a Roland – every player knows there’s a magical potion concocted of guitars, amps, and fingers.

But, is it possible to cover the sonic spectrum of all genres with just five classic tube amps? We’d like to think so… within reason, at least. If you’re looking to populate an arsenal that can cover all stylistic bases, here are five outstanding amp choices amid the spectrum.

Killer Tweed: 1958 Fender 5F4 Super Amp
The 5E3 Deluxe and 5F6-A Bassman more often get props as the ideal small and large tweed amps, but the Super is something of a cross between the two, and arguably more versatile as a result. The Super has more headroom and better articulation than the Deluxe, with a feel-enhancing cathode-follow tone stack besides, but it’s also restrained enough in the output department (30-ish watts) to let you hit the sweet spot in many venues where a Bassman will just get you into trouble (which is the case in more and more music rooms these days). The beauty of these amps is that while they give a big dose of the chunky, open 6L6 tone, their output is still low enough to cut it at many smaller clubs and in the studio. The two 10″ Jensen Alnico speakers aren’t the most efficient drivers by today’s standards, but offer a fast, lively response, and a snappy, slightly gritty tone that benefits a range of rootsy styles.

Two long-standing legends tell how the Super was Leo Fender’s favorite amp, and that it was designed to partner with the Telecaster. And while there’s no documentation, it’s easy to believe. Amp usage in the ’50s often wasn’t well-recorded – they were just those tweed suitcases you plugged your guitar into – but countless early rock-and-roll and country players did their thing on tweed Supers, and they can be heard all over classic recordings from the era.

Aside from bagging an original, the circuit is represented accurately in reproductions from several sources including Victoria’s 35210. The narrow-panel Pro, Bandmaster, and low-powered Twin are essentially the same amp with different speaker configurations.

Class-A Contender: 1964 Vox AC30/6 “Top Boost”
In the Class A category, you can’t do much better than a mid-’60s Vox AC30 with Top Boost. This wasn’t the first version of the AC30 to hit the scene, and earlier AC30s without Top Boost can also sound extremely good, but that simple two-knob EQ stage added zing that coalesced what we think of as “Vox tone.”

JMI engineer Dick Denney devised the Top Boost circuit in 1961 (some say he copied a Gibson circuit) and it was available as a back-to-factory modification until it became a standard upgrade on the control panel in late ’63. Pump that lively, articulate ECC83-based preamp through the four-EL84 output stage driving upward of 35 watts, and there’s a lot of tone. From crisp, clean, and chiming to chewy and snarling, the AC30 has a great range, too, with great multi-dimensional harmonic content throughout, all made sweeter by a pair of Celesion G12 Alnico-magnet speakers.

Well-documented as the sound of The Shadows and many early recordings by The Beatles, it also backed a great deal of Brian May’s cranked Queen soloing, Tom Petty and Mike Campbell’s chimey Yank-rock crunch, and Peter Buck’s toothsome jangle with R.E.M., to name but a few. Aside from the modern renditions available from Vox and the revitalized JMI’s contemporary clones, the AC30 receives homage in amps like the Matchless DC30, TopHat King Royale, or Bruno Underground 30.

Five Classic Amps
1964 Fender Deluxe Reverb
Do-It-All Club Amp: 1964 Fender Deluxe Reverb
Fender’s Deluxe Reverb, introduced late 1963, has become a standard on the scene for several good reasons. Though there are many contenders, this is arguably the ultimate club amp – the ideal grab-and-go for virtually any gig with minimal fuss.

A lot of studio players have preferred the Princeton Reverb – which also has a two-6V6 output stage, tremolo, and reverb – but the Deluxe’s heftier 22-watt output and larger speaker (12″ versus 10″) give it enough firmness and headroom to hold its onions for pristine clean tones at reasonable volumes if you don’t push it too hard, and pedal-steel players have even been known to get away with a Deluxe Reverb in some venues. That said, it’s still not difficult to get it to break up sweetly without blowing the doors off most establishments.

Without jumping to modern channel-switchers and exotic multi-effects units, a Deluxe Reverb can handle anything this side of metal. Heard all over classic pop and country recordings of the ’60s and ’70s (Roy Buchanan cranked one into ecstasy for his extreme Tele wrangling), it has long been a favorite of indie-roots-leaning Telecaster player Chuck Prophet, and Blink-182’s Tom Delonge, who uses a pair of ’em.

Rock God: 1968 Marshall Model 1959 JMP100 Super Lead
If you’re looking for one amp to define the classic-rock sound, there really can be no other choice. Nothing is quite like the wind-in-your-hair, flap-your-trouser-leg experience of a raging “plexi” full stack. It’s the tone that launched legend upon legend, establishing an archetypal rock voice in the process.

Jim Marshall and cohorts famously derived their first amp of 1962 from Fender’s 5F6-A Bassman circuit of the late ’50s, and it had evolved just a little by the plexi era of the late ’60s (mostly via the addition of two more EL34 tubes in the output section), but all that bluster, crunch, and crispy high-end wail through eight 12″ Celestion Greenbacks takes us a lot further from late-’50s tweed territory than a decade’s worth of semi-evolution might imply. Not only extremely powerful, but superbly touch-sensitive, a good Super Lead can deliver everything from the more contemplative moments of Jimi Hendrix’s down-tempo blues musings to the thick and creamy Cream-era lead work of Eric Clapton and Eddie Van Halen’s game-changing tones on “Running With The Devil” and “Eruption” (with a little help from a Variac and an amazing pair of hands).

Still the first choice of died-in-the-wool rockers, this classic is available in reissue form or in clones and modified renditions from the likes of Germino, Rockitt Retro, TopHat, and many others.

Five Classic Amps
(TOP) A 1984 Mesa/Boogie Mark IIC+and a 1968 Marshall Model 1959 JMP100 Super Lead. Mesa/Boogie Mark IIC+: Matt Hertel, courtesy of Todd Duane.
California Screamin’: 1984 Mesa/Boogie Mark IIC+
Through the ’70s, when players began to develop a taste for that cranked-up rock lead tone (a la the Marshall Super Lead) at volumes that wouldn’t cause a joint to crumble, they often turned to one of Randall Smith’s Mesa/Boogie creations.

Early renditions (dubbed Mark I after the Mark II came along circa 1979) were best known as the source of Carlos Santana’s characteristic singing guitar tone, but in the opinions of many Boogie fans, the original compact 1×12 combo line reached its zenith in the Mark IIC+ of 1984/’85. For this iteration, Mesa’s Doug West and engineer Mike Bendinelli ramped up the gain to scorched-earth proportions, and developed a major cult following in the process.

The only “footswitchable” amp of our five classics, it seems reasonable that from 31 years worth of hindsight we can allow it “vintage” status – and in many ways it was a creation born at the end of an era that wears that tag. Created for tone more than for features, the Mark IIC+ was nevertheless an extremely versatile amp for its day, with a very respectable clean tone in addition to its sizzling lead tone. Factor in extras such as reverb, effects loop, graphic EQ, and dual output levels from its Class-A setting (15 watts) or its SimulClass blended Class-A/Class-AB setting (80 watts) and it’s easy to comprehend the range of its prominent usage – from Metallica’s “Master Of Puppets” to a major slathering by John Petrucci in Dream Theater.

Five Classic AmpsWHAT’S IN A TUBE?

The way a tube functions is, on one hand, ingeniously simple, yet on the other is influenced by a complex range of factors that make up the broad range of tones that an electric guitar is capable of producing through a tube amplifier.

Most of us understand that the patterns within the grooves of a vinyl LP or the magnetically arranged particles on the surface of an audio cassette or reel-to-reel tape are not the sound of the music itself, but an analogous physical representation of that sound, which can be translated back to a startlingly close rendition of an actual performance when translated by a record player or tape deck via a stereo amplifier. Similarly, the tubes in a guitar amp don’t take the actual sound of your electric guitar and “expand” it; they amplify the guitar by producing a flow of electrical current that provides an analogous representation of the frequency, timbre, volume, and dynamics of your playing, with the guitar acting as the “controller” of that flow.

Confusing? A quick look at what goes on inside tubes and how they work can bring the process into sharper focus.

Amplification occurs in any tube amp in several stages; preamp tubes convert the puny electrical signal of less than one volt AC generated by a guitar’s pickups into a stronger signal, which is in turn converted to an even stronger signal by the output (a.k.a. power) tubes, which, with the help of an output transformer, is converted to a current capable of driving a speaker. There can also be other stages for shaping tone and adding effects, but the tubes truly do the real amplification work, and everything else in the amp – resistors, capacitors, and power-supply components – is there to enable the tubes to function.

Most tubes in guitar amps use four basic elements – the cathode, the plate (a.k.a. “anode”), the grid (a.k.a. “control grid”), and the filament (a.k.a. “heater”). Despite carrying these four elements, many simpler tubes are called triodes, a designation that ignores the filament because all tubes need to be heated to operate. Many tubes have further elements, usually extra grids to help control or stabilize function. Those with four elements plus heater are called tetrodes, while those with five are called pentodes.

Put simply, when a tube’s cathode is heated by its heater, electrons begin to flow from it, through the control grid, and onto the plate (which is in a negative state relative to the cathode, and thus attracts these electrons). The absorption of electrons on the plate determines the amplified signal that is sent onward from the plate’s external pin connection to the next stage of the amplifier.

Without delving too deeply in the physics of the process, here’s a breakdown of the basic function of the three crucial elements.

Five Classic Amps
(LEFT) The most common preamp tubes used in guitar amps are called “dual triodes,” because they contain two independent amplification units in one glass envelope. Each of these two individual triodes employs a plate (anode), grid, and cathode. This description covers the popular 12AX7 (ECC83 in the UK), as well as the 12AT7, 12AY7, 12AU7, 5751 and others. (MIDDLE) The tubes used in guitars amps’ output stages are most commonly called “pentodes,” because they contain a screen grid and a suppressor grid in addition to the triode’s control grid. These added elements essentially help to overcome capacitance between the control grid and the plate. (RIGHT) Indirectly-heated rectifier tubes contain three elements – two plates, a heater, and a cathode – while directly-heated rectifiers contain just heater and plates. These tubes don’t amplify the signal, but convert the power transformer’s AC voltage to the DC voltage that the preamp and output tubes run on.
Control Grid: The tube’s “input,” where incoming signal from the guitar (or a tube earlier in the signal chain, i.e. an outboard drive/OD pedal) is applied. In most common audio tubes, the control grid is like a tiny ladder of plated wire wound around two posts, often made of copper (this structure is usually not visible within the tube, since it is often obscured by the plate). The control grid’s function is to control the electrons that flow through it, according to the signal applied (which is analogous to the notes played on the guitar), and the result determines frequency and amplitude of the onward signal generated by the plate.

Cathode: Usually a nickel tube coated in oxide, the cathode is positioned close to (or surrounding) the heater filament, and must be heated glowing-hot to function. In its heated state, the oxides on the cathode “boil off” electrons into the vacuum/empty space within the tube, and they then flow to the plate via the control grid. The cathode is also obscured by the plate, and so not visible from outside the tube, but you can usually see the heater glowing within it.

Anode/Plate: The plate is the tube’s “output,” and is an electrode to which the electrons flow from the cathode – via the control grid – and where they are absorbed to determine the amplified signal that is passed onward in the circuit via the tube’s plate connection pin. Although the plate is not heated the way the cathode is, the process of absorbing electrons can make it very hot, so this component is made from thin, relatively broad plates of metal that radiate heat through the tube’s glass envelope. The plate (usually gray or black) is the largest component you can see within the tube.

In addition to these essential components, most tubes also have a thin filament or “halo” shaped element called a getter – usually seen at the top of the tube – which helps to burn off stray oxygen within the envelope to maintain the vacuum, as well as structural components such as mica insulators and spacers and other structural parts.

With this overview of the tube’s components in mind, it should be a little easier to understand how they do what they do. Essentially, the AC signal from a guitar’s pickup(s) is the “trigger” that gets the tube going; it tells the control grid the frequency and amplitude at which it should let the electrons flow from cathode to plate – it controls the electronic analogy (hence “analog sound”) of your playing, rather than piping through the actual sound of the guitar and enlarging it, the way a megaphone enlarges the sound of a human voice speaking into it. The ways that tubes do this job and the ways the other components shape their function all help determine the final shape of your guitar tone.

Rectifier tubes are not amplification tubes, so the same rules don’t apply. The rectifier tubes commonly used in guitar amps are “diodes” (or twin-diodes, in fact), meaning that rather than containing the three elements of a triode, they only contain two: anode/plate and cathode. In many rectifier tubes such as the 5Y3 and 5R4, called “directly heated” rectifiers, the heater plays the part of the cathode, too, and electrons flow from heater to plate. “Indirectly heated” rectifier tubes such as the GZ34 and 5AR4 have a cathode placed close to the heater (and heated by it), from which electrons flow to the plate. Essentially, rectifier tubes combine two streams of AC current from the amp’s power transformer into a single stream of DC current that goes out via the connection to the cathode and onward through the amp to feed the amplification tubes. In many amps, solidstate diodes are used in place of tube rectifiers. – Dave Hunter

This article originally appeared in VG July 2015 issue. All copyrights are by the author and Vintage Guitar magazine. Unauthorized replication or use is strictly prohibited.