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Vacuum Tubes – Favorite Power Tubes for Guitar Amps

September 23rd, 2013

Two 6V6 with a GZ-34 rectifier is a great recipe for clean to crunchy rock and roots music

Despite all the progress in digital modeling and analog circuit design, for some people a guitar amp isn’t a guitar amp without a few glowing glass bottles heating up the room. Technically obsolete but sonically beloved, tubes are still with us. And the crazy thing is they all sound different from type to type, and even brand to brand. Depending on your point of view this is a tweaker’s delight or nightmare.

Truth be told, there is some great sounding digital stuff, and if you are generally immersed in very high gain sounds or lots of effects, I’m not sure tubes are essential. There is just so much other signal processing going on that the subtle qualities of vacuum tubes can get lost. My friend’s Eleven Rack sounds pretty darn good pounding out raging “SLO” crunch, but as a semi-clean Fender Deluxe? Not so much. So if you are still chasing clean to slightly dirty tones, I think analog and vacuum tubes still hold the edge. Speaking of “The Edge:” By the time his guitar has run through fifty feet of effects and remote switching gear, does it matter that it’s plugged into a vintage Vox? No, especially not in a stadium. Sometimes it’s all about what you’re seen playing, which is why most of those stacks at a typical concert aren’t even plugged in (unless you are Yngwie).

If you are deciding to go the tube route, or are looking at a new tube amp, you also have to think about what types of power tubes. Preamp tubes are almost always the venerable 12AX7 — with an occasional EF-86 — so that choice is usually made for you. But with power tubes you have some decisions to make. Here are some comments and thoughts:

6V6 – The mainstay of the 30 watt and under Fender amplifiers, especially from the Tweed and Blackface era. Some of the newer small Fenders today like the Junior and Deville series use EL-84, so check under the hood. Sweet sounding with a high end that is complex and not overly bright, they are a great tube for small amplifiers. Maligned by some as not having strong bass response, that can be as much cabinet size and circuit design as the tube itself. A great tube for Strats and Teles. Less popular today than the EL-84, but a Dr. Z Remedy on half power is one of my all-time favorites. The ValveTrain Trenton is also another great recent 6V6 amp, and Rivera is also a proponent of this tube (they don’t make an EL-84 amplifier).

6L6 – The mainstay of the larger American amplifiers, the 6L6 can put out up to 25 watts per tube and is found in higher powered amps like Twin Reverbs, and many Mesa amplifiers. A little harder sounding and less complex than a 6V6, but it’s got a lot of low end. Great for chunky tones, sparkling loud cleans, and high gain.

5881 – A lower output alternative to the 6L6, the 5881 is often used interchangeably and is felt to have a little more delicate top end, and be a touch more musical. Amps with a 6L6 may be running at higher voltages not suitable for a 5881, so do your homework before you swap.

EL-84 – Developed by Philips, probably the most popular tube for amps under 30 watts, and the darling of boutique builders. Many of the small Fender amps today use this “European” tube rather than the 6V6. Personally not my favorite, especially not for gigging. They do have a lovely round “bouncy” tone that is really cool at low volumes, but these tubes tend to get shrill when cranked up, and have flubby, weak bass. YouTube is full of videos of people playing totally cranked small EL-84 amps through attenuators in their home studios. That may be fun, but not for your vocalist, or the crowd. This tube may be the “sound” of a Vox, but gimme a 6V6 any day.

EL-34 – This tube is the crunch of the big Marshall amplifiers: Punchy, with a strong upper midrange bite and lots of harmonic content. Most big Mesa 6L6 amps will also accept the EL-34, and it’s worth making the swap.  The problem is that any Class AB amp with these tubes is going to be pushing 50 watts or more. So they are fun but loud. There are some specialty Class A amps that will take a single EL-34, so you can have some fun without peeling the paint.

Wrap Up – Depending on the size range of amplifier you are shopping for, your choice of tube may be per-determined by the power rating. On the sub 40 watt end, my recommendation would be the 6V6. Not as ubiquitous as EL-84, but worth it for overall sound quality and flexibility. The 6V6 has a different pin arrangement than the EL-84, so they cannot be swapped unless you purchase adapters.

For larger amps, my pick is the EL-34, and a number of big rigs can flip a switch and accept an EL-34 or 6L6. For a 6L6 amp that cannot use an EL-34, check with the manufacturer and see if it is compatible with the 5881. This can be a nice tweak for a little less headroom and power output. A lower-voltage Fender Bassman running 5881’s is a delectable clean-to-mildly-crunchy tone machine.

For amp offerings at Upfront Guitars:  www.upfrontguitars.com

Pedal Amps – What’s a Pedal Amp?

September 22nd, 2013

Nearly every guitar player today uses some type of effect pedal, either for practice, recording or  playing live. Safe to say there is hardly anyone who does not own some type of effect pedal, making them both a great market for manufacturers, but also a real consideration when deciding what type of amplifier to use.

One of the frequent questions asked these days on the gear pages is what’s a good “Pedal Amp?” So what is a Pedal Amp? I would define a Pedal Amp as an amplifier that does not add extreme tonal coloration, and is able to handle high signal inputs without adding additional coloration or distortions. To some that does not sound like a particularly good amplifier, as for many old-school players the amplifier is an essential part of the sound equation. But for players that increasingly use various types of effects and digital modeling, the amplifier becomes more of an “amplification system” and less of a tone source.

Going back a few decades, the early amplifiers were instrumental to the developing sound of rock music. The happy accident of distortion, and then the use of lots of distortion as the essential rock guitar sound was not what the Founding Fathers intended. But as recording techniques, sound systems, and musical styles evolved, the concept of a pure unaffected guitar tone became increasingly rare. From the early days of cranking up small wattage amplifiers to get grindy tone, practically everyone today — well maybe not Neil Young — is using some type of effect to generate anything from mild to insane distortion. And while there are zillions of multi-channel amps out there, for flexibility’s sake pedals just allow much more room to mix and match tone.

So what makes a good Pedal Amp? In a word: Headroom. From a design standpoint, early amplifiers were notoriously short of headroom, both in the preamp and power sections. This of course gave them their warm creamy tone, but pump a high gain pedal into a Fender Tweed and the net result will be mushy distortion with very loose undefined low end. Practically speaking the pedal is creating distortion, and the higher input signal from the pedal is also distorting the preamp of the guitar amplifier. Distortion-on-distortion is not always desirable or musical.

Generally speaking, low powered cathode biased amplifiers (Tweeds, small Vox’s, lots of other low power EL-84 amplifiers) are not super candidates for pedals that have the capability of generating fairly high input levels. Even the relatively brawny 45 watt Fender Bassman won’t handle a lot of input signal without getting floppy. Hot input signals can come from distortion pedals or frequency modulation pedals (chorus, flangers) that tend to increase the signal level. Now boost pedals are made specifically to increase the signal, often for the purpose of overdriving the front end of an amplifier. But a boost pedal it typically only increasing the signal, and not adding its own distortion or other artifacts.

The boutique amp craze, with its plethora low power Tweed and Vox inspired designs (Dr. Z, Matchless, Badd Cat, Victoria etc) created some awesome sounding amplifiers that well-heeled baby boomers were craving. However they were not necessarily great at handling pedals, and even at 18 watts a Maz 18 is still damn loud. And this inspired the attenuator craze….and now everybody just buys pedals.

Fixed biased amplifiers — like Fender Blackface or similar designs — by virtue of their circuit topology have higher headroom and tolerate pedals better. Fender of course was trying to make louder and cleaner amplifiers to fill the larger venues that rock bands were playing. For that reason amplifiers that follow the higher powered Fender Blackface 6L6 tube lineage tend to be pretty good pedal amplifiers.

Once amplifier designers discovered master volume techniques and cascading gain (preamp distortion) techniques, amplifier designs became “stiffer” cleaner and louder. The general elimination of tube rectifiers in favor of diode rectifiers also increased headroom, and made the amplifiers sag less, and play cleaner under heavy loads. Distortion was now a design goal, not a by-product of marginal design or power handling capability. But to some, all these improvements — including dreaded solid state — took away some of the “organic” nature of the early amplifier sound.

Fast forward to the boutique amp craze and builders were putting all this “marginal” stuff back into amplifiers: Cathode bias, low power, and tube rectifiers. And at the opposite end of the spectrum some players are now using a totally digital preamp source — like an Axe Effect Fractal or Eleven Rack — and a powered full-range speaker system from JBL, QSC, or EV.

So back to the original topic: Good Pedal Amps tend to be more modern or higher powered designs that can tolerate strong signal inputs, and if they use a tube power amp section, have a solid state rectifier. If you are playing live or play at high volumes and want to use gain pedals, it’s advisable to avoid lower powered designs in the mold of a Tweed or Vox. Nothing against these amps — Robert Cray through a Matchless is a great sound — but it’s not a pedal sound. There are always exceptions to the rules of course, and some of the boutique designs using the EF-86 preamp tube (Dr Z. Z-28 for example) have quite of bit of clean headroom despite modest power outputs. It’s always dangerous to generalize.

Speaking of which, what about the Mesa Dual and Triple-Rec designs. Don’t they also violate the low power/tube rectifier rule? Yes, sort of. Up around 100 watts, tube rectifiers are pretty marginal AC-to-DC converters for creating the high voltage DC that power tubes need. By wiring two rectifiers in parallel, each rectifier is only carrying half the current, and therefore can share the load and maintain headroom (Fender did this on some 50’s amps for the same reason). A Triple-Rec adds one more rectifier for handling even higher powered designs. Mesa could have just used solid state diodes, but a Mesa Diode Roadking lacks marketing pizazz. Most Mesa — and modern metal — amplifiers are characterized by very “clean” clean channels and the distortion is produced by various combinations of tube and solid state wizardry.

Finally, here’s a personal example with the two amps I like to play the most: A Fender Reissue Bassman, and a Dr. Z Remedy head plugged into a Mojo Pine 4×10 cabinet with Jensen P10R/Eminence Blueframe speakers. Both are using virtually identical speaker arrangements, speakers, and cabinet materials. But the Bassman is an early cathode bias design with a tube rectifier, and the Remedy is a solid state rectifier design using four 6V6 tubes (not a “reissue” design but billed as having Marshall Plexi-style tone). They both have the same power output, about 40 watts. I love the Bassman tone, but in gigging situations using pedals for various levels of gain and effects, the amp loses definition, attack, and can get sloppy. Even on half power, the Remedy has better attack, low end firmness, and is overall tighter. Crunchy gain is crunchy gain. On full power the Remedy is really too clean for most situations except outdoor gigs. But both are 40 watt amps.

My general rule of thumb for any amplifier selection is to find the best clean tone that makes you happy and then go pedal shopping. If your favorite tone is clean to slightly crunchy, you may never need pedals and a smaller lowered powered “old school” amplifier may be the ticket. But if you are like most players, make sure the amplifier of your dreams has sufficiently stout headroom to serve as a suitable platform for whatever pedals you decide to use down the road.

For more information on platform and pedal options at Upfront Guitars:  www.upfrontguitars.com