The Difference Between Class A and Class AB Tube Amps

You’ve seen various tube amp descriptions that read Class A or Class AB amplifier, but what does any of that mean? And why should you care?

KT88 Tubes

What’s the difference between class A and class AB tube amps?

Check out this break down of the differences for the quick answer. The detailed explanation and some examples follow further on….

Class “A” Amplifiers

Advantages:

  • The tube always warmed up and ready to amplify the signal.
  • Tube does not have to “wake up” from a “ready” state.
  • Class “A” amps have greater output than Class “AB” amps. If two EL84 output tubes in a Class A design may produce only 10 watts of output power, then the same two tubes in a Class AB design might produce 50 watts.
  • Smooth compression.
  • Less headroom. (NOTE: This is a disadvantage to some musicians who are looking for good, clean tone at higher volumes).
  • More responsive to the touch – i.e.: feels good to play.
  • Class A amps with EL84 tubes in push-pull design emphasize high order harmonics. This emphasis makes the amp “sing”.

Disadvantages:

  • Keeping the tubes warmed ready requires more current at all times. This constant current leads to shorter tube life.
  • Lower power rating than a Class “AB” amp with the same tube configuration.

 Class “AB” Amplifiers

Advantages:

  • Longer tube life.
  • More headroom – cleaner cleans at higher volume.
  • Tighter bass response – less prone to “muddy” tone.
  • More efficient use of power.

Disadvantages:

  • Not as responsive as a Class “A” amp.
  • Tone won’t “break up” as easy.

Class A vs Class AB, the Detailed Explanation.

The three major parts that make an amplifier tube are: the Cathode, the Grid and the Plate. The Cathode heats up when voltage hits the tube, causing a cloud of electrons to form. The Plate has a positive charge, which causes the negatively charged electrons to flow toward it. The Grid controls this flow of electrons. It is also the audio signal input for the tube.

An audio signal entering the tube causes a change in voltage at the Grid. This change in voltage changes the flow of electrons  and causes amplification.

The behavior of electrons described above is an example of a Class A amplifier. These amps apply a positive voltage to the Grid. Class AB amplifiers apply a negative “bias” voltage to the grid. This bias causes the electrons in the cloud to avoid the Plate. This is the standby mode of the tube.

The voltage of the audio signal entering the Grid causes the voltage on the Plate to change from negative to positive. This attracts the electrons in the cloud and causes them to flow to the plate. The tube in the Class AB amp then behaves like a Class A described above.

The need to change the charge of the plate from positive to negative causes the Class AB amplifier to feel less responsive than a Class A amp. But it also means the tube components aren’t in full use even when a signal is not passing through. This means the tubes generally last longer.

Class A amplifiers

Bugera V5 Infinium

Looking for a low watt amp that won’t blast a hole in your eardrums or your budget? Bugera is for you.

The Bugera V5 Infinium is a 5 watt all tube amp for less than $200.

Let that sink in for a moment.

For the price of a really good solid state amp, you can get an all tube amp. But that’s not all.

  • The Bugera V5 is a Class A amp driven by a single EL84 tube with a single 12AX7 tube in the preamp.
  • Specially designed 8 inch Turbosound speaker. (This is a classic combination for the British crunch and buttery blues tone)
  • Power attenuator, which effectively lets you decrease the headroom even more and get killer overdrive or distortion at a lower volume
  • Digital reverb capable of dialing in everything from subtle to downright cavernous.

Where the Bugera V5 Infinium really makes its mark is with it’s Tube Life Multiplier technology. According to Bugera, this tech ensures:

.. greater reliability and consistent tone over the lifespan of your tubes by monitoring the performance of each of the amplifier’s output tubes and maintaining them at their ideal operating point for an evenly distributed load.

There’s also an LED next to each tube that lets you know when it’s about to die.

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Ibanez TSA5TVR

This stylish little beast is another micro amp, 5 watts and an 8-inch speaker… and a built-in Tubescreamer circuit!

With a retro look of a 1950’s television it harkens back to a simpler age when televisions were the furniture centerpiece in a room; meant to attract attention and start a conversion. The Ibanez TSA5TVR is an attention-getter as well.

  • 8″ Jensen C8R speaker.
  • Ruby 6V6 and 12AX7 tubes.
  • Lush Accutronics spring reverb
  • Built-in Tubescreamer – complete with overdrive, tone, and level knobs

The TSA5TVR gives you everything from slight, dirty gain for blues and rock all the way up to high gain for lightly compressed distortion. It’s a small package that sounds much bigger.

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Peavey ValveKing Royal 8

The ValveKing gives you punchy dynamics and classic rock tones that sound much larger than its small package.

  • 5 watts
  • One EL84 output tube
  • One 12AX7 preamp tube
  • Single-channel design
  • Dual ¼” inputs
  • Master volume and gain controls

Rollback the gain and crank up the master volume to get that great class A “breakup” power-amp tone. Or crank the gain and dial back the master volume and you’ve got raging  preamp distortion.

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It’s that easy.

Orange Tiny Terror TT15C-12

This loud and proud Orange Terror owes it’s punch to a special reissue of the Celestion G12H 12 inch speaker. The G12H is a mix of the Vintage 30 and Greenback speakers and produces thick, warm and sugary sweet tones.

  • 15 watts, Switchable to 7 watts
  • Single Celestion G12H 12″ Speaker
  • Gain, tone, volume controls
  • 2 x EL84; 2 x ECC83/12AX7 tubes

The cool thing about the TT15C is that it’s switchable from 15w to 7w, which makes it great for break up or recording.

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Class AB amplifiers

Vox Night Train NT15C1-CL

 

The Night Train is a big sounding Class AB amp covers all the Vox tones from clean to crunch and all the way to high-gain. The classic Vox look with suitcase style handles makes the package complete.

  • 3 – 12AX7 tubes in the preamp section
  • 2 – EL84 tubes in the power section
  • Two-channel BRIGHT/GIRTH
  • The THICK switch provides an additional gain boost on the BRIGHT channel
  • Reverb
  • 15 Watts
  • 12 inch Celestion G12M Greenback speaker
  • Inputs/Outputs: Guitar Input, FX Send, FX Return, Foot switch
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Marshall DSL15C

The DSL15C is Marshall’s 15w, all tube combo amp. It’s compact, but packs a punch with classic EL84 tube tone. The DSL15C has two 6L6 tubes in the power section, but the preamp is all EL84s.. three of them to be exact.

15 watts may not sound like a lot, but for a tube amp it’s plenty loud for practice or small gigs. In fact, one of the things that makes the DSL15C so cool is that it has a pentode/triode switch for selecting the full 15w or a half 7.5w of output. That’s a great bit of versatility, and long time readers of this blog know that versatility is a big deal here.

The DSL15C also features a foot switchable gain channel that lets you switch between classic gain and ultra gain. Also present is a “deep switch” that gives your tone a bit of a low end boost.

With all these features and a 12 inch Celestial G12E speaker and built in reverb, the DSL15C captures the classic EL84 British sound in a tight little tone package.

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Laney Cub 12

The Laney Cub 12 has a 15w and <1w input. Jack into the 15w input and you get the full throated roar, jack into the <1w and you get a more manageable volume for practice, with substantially less headroom. This means that you can get those dreamy, creamy British overdrive tones that EL84s are known for at a much lower volume.

  • 15 watt all tube class A/B amplifier
  • Three ECC83 tubes in the pre amp and two EL84s in the power amp stage
  • Digital reverb (Tone and volume (as with the Cubs 8 and 10) and bass, middle treble EQ and gain control
  • FX loop
  • 12 inch Celestion speaker

The tube configuration gives the Cub 12 a much bigger voice than the Cub 8 and 10. Also, if 12 inches of Celestion isn’t enough for you, there’s also an external speaker out jack.

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7 Of The Best Blues Amps for Guitar (under $1000).

What makes for good blues amps? It’s a question with many answers, but  sustain, crunchy overdrive, good clean tone and a certain look are all part of the formula. It’s true that the blues can be played on just about any amp, but here are 7 amps that have what it takes to make for great blues amps – and each is under $1,000.

7 Great Guitar Amps for Blues.

Vox Amps

The most famous Vox amps, the AC15 and AC30, don’t look the part of classic blues amps, but they play the part just fine.

Sure, the Vox AC 30 is renowned for it’s jangly, Beatles vibe and searing treble tone of Brian May, but Brian Jones got plenty of dirty bluesy tone when he used his on Rolling Stones records. And Rory Gallagher paired his with a Dallas Rangemaster treble booster to craft his signature sound.

vox-valvetronix-20w

In short, the Vox AC30 delivers the blues goods, especially when you crank it. But that could be a problem at times because a cranked AC30 (or even AC15) can be LOUD.

Also, the AC30 is expensive, at around $1,200. The AC15 is more affordable, in the $600 range.

But if you’re on a budget or have to keep an eye on volume from time to time, then you should check out the Vox Valvetronix series.

I recommend either the Vox Valvetronix VT20 or Vox Valvetronix VT60. They are essentially the same amp, but the Vox Valvetronix VT20 is a 20w 1×8 combo amp and the Vox Valvetronix VT40 is the 60w, 1×10 version.

Both are solid state, modeling amps based on Vox Valve Reactor technology for true tube modeling realism.

Both come with 99 presets (33 song presets, 33 basic presets and 33 presets with effects.), and a ton of useful features like mp3/AUX in, headphone out, and each is foot-switchable and programmable.

Check VT20 Price  Check VT60 Price

Demo

Fender Amps

Fender Excelsior

The Fender Excelsior is a 13w, 1×15 all-tube combo amp with a unique 1950’s vibe, sound and style all its own.

The Excelsior is powered by dual 12ZX7 tubes in the preamp and dual 6V6 tubes in the power output section and houses a 15″ Eminence Legend speaker.

The Excelsior also has onboard tremelo and a bright/dark tone switch for treble or bass emphasis. It’s one of the great and simple blues amps that takes pedals well and it’s also great for harmonica too.

The Excelsior can also drive an external speaker cabinet, if the 15″ Legend isn’t enough for you.

Oh, and they’re part of Fender’s Pawn Shop series, which means not were made, so they will be collectible.

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Here’s the Excelsior amp in a blues style demo

And another:

 

fender-excelsior-antique-blush

fender-excelsior-brown

fender-excelsior-surf-green

fender-excelsior-sonic-blue-angled

Fender Blues Deluxe Reissue 40-Watt 1×12-Inch Guitar Combo Amp – Tweed

To many players, nothing says blues amp quite like a Fender Blues Deluxe, in Tweed.

Tweed is just a classic, vintage blues look – and tone.

Fender is renowned for their clean tones, and the Fender Blues Deluxe is no exception. It delivers 40 watts of tube driven tone with plenty of headroom for clean tone and great bluesy breakup when it’s driven. It also has on-board spring reverb, an essential blues effect.

The 12″ Eminence special-design speaker gives plenty of punch and offers enhanced midrange to help you break through any mix.

fender-blues-deluxe-40w

The Fender Blues Deluxe is powered by two 6L6 Groove Tubes output tubes and three 12AX7 preamp tubes. In addition to the spring reverb, the Fender Blues Deluxe also features an effects loop, two-button channel footswitch, classic tweed covering and chicken head knobs on a chrome control panel.

The Fender Blues Deluxe makes a great blues, rock and country amp.

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Demo

Fender Hot Rod Series Blues Junior NOS 15W 1×12 Tube Guitar Combo Amp

The Fender Blues Junior NOS is a modern blues machine built to vintage specs and using new, old stock parts.

The Fender Hot Rod Series Blues Junior NOS 15W 1×12 Tube Guitar Combo Amp is an all tube (2 EL84 Groove Tube output tubes and 3 – 12AX7 preamp tubes), 15w combo featuring a single 12″ Jensen C12 speaker. It has a single channel with “Fat” Switch, reverb, and a footswitch jack so you can toggle the Fat switch on/off more easily. It’s got vintage knobs for reverb, master, middle, bass and treble control.

fender-hot-rod-blues-junior

Tweed finish with pinstripe grille cloth complete the vintage blues look.

The Fender Hot Rod Series Blues Junior NOS 15W 1×12 Tube Guitar Combo Amp is a great blues amp for the price, but it’s also good for jazz and classic rock.

 

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Demo

Peavey Amps

Peavey has a reputation for metal amps, but they also make some of the best blues amps around. Just check these out..

Peavey Delta Blues 210 guitar Amplifier with Tremolo

The Peavey Delta Blues 210 is a guitar combo amp with tremolo and reverb.

Peavey-Delta-Blues-210-guitar-Amplifier-Tremolo

This is a great amp for those who dig the Fender sound, but want something a bit different in style or a bit less money. While the Peavey Delta Blues 210 is inspired by Fender, it is its own beast. It handles clean jazz and country tones all the way up to classic rock overdrive.

Packed with 2 10″ Blue Marvel speakers, three 12AX7 and four EL84 tubes and on board tremelo and reverb, the Peavey Delta Blues 210 definitely makes the killer blues amps list.

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Demo

Peavey Delta Blue 115 (II) 1×15″ 30-Watt Tube Combo Amp

eavey-Delta-Blue-115-1x15-30-Watt-Tube-Combo-AmpNext in the Peavey blues amps lineup is the Delta Blue 115. It’s a 30w combo amp with a single 15″ speaker. With 3 12AX7 and 4 EL84 tubes, it’s powerful enough for gigging and built for blues with onboard spring reverb and tremolo.

The Peavey Delta Blue 115 also features an effects loop, optional footswitch, and an output for an extension cabinet.

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Demo

Marshall Amps

Marshall Class5 – 1×10 Combo

One of my all time dream amps is the Marshall 1962 Bluesbreaker. This kind of sucks though, because at $2,499 it is well outside my budget. (That’s why it’s a still a dream)

But luckily, Marshall has a similar blues amp that fits the budget player much better, coming in at around the $400 mark.

Marshall-Class5-1x10-Combo

The Marshall Class 5 – 1×10 Combo is, as the name suggests, a 5w, 1×10 all tube combo amp that’s perfect for home, studio and small gigs. It’s got a headphone output jack, and Volume, Treble, Middle, and Bass controls.

What you get with the Marshall Class 5 is pure Marshall tone – from bluesy cleans to plexi style crunch, and everything in between. All of that without being a 200lb behemoth, stacked to blow the roof off.

With 2 ECC83 pre-amp tubes, and 1 EL84 power tube, it’s light but powerful enough to get you great tone where ever you are.

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Demo

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