At first glance you will see one very noticeable feature on the Dirty Boy. That feature is the “built in Variac” placed right in the center of the amplifiers front section. The dial is large and the control dial plate is large for easy visual reference. This is the heart of the amp. Not only does the variac control the Dirty Boys over all power level, but unlike anything you might have experienced, the Variac creates completely different sound characteristics not obtained by standard amp topology.

Look closer and you will see an array of controls, some are familiar such as Guitar Volume, Treble, Midrange, Bass and Presence. The ones you are probably not familiar with are ones that are not found on amps generally due to the fact that they are fixed assets which the user has up until now, never had the ability to change. If you were to take your guitar amp in for service you might get it back sounding different then when you took it in. That could be a result of a cold bias or a hot bias or something in between. Frankly the bias control is an enormously important part of the amps sound and behavior. We have let the monster out of the box so to speak and brought you the flexibility of making this one of your own custom controls. You can now adjust the power tube bias, through a front panel user control, to your liking and not depend on a tech to do it for you. You know the sound in your head, now you have one more tool to get it. We will cover the bias control in detail later, for now we are going to introduce you to the Dirty Boy’s over all control scheme.

The next control you probably do not recognize would be an adjustable feedback. Typically, just like the “bias adjustment”, you the user would not have access to the feedback setting. The amplifier’s feedback is fixed by a set resistor and is sometimes changed by techs in a custom modification to either increase or decrease gain and response. Now you no longer have to guess what that means to you and your sound. We have brought that to you as a front panel user control. The adjustable feedback control will influence your sound in a drastic way. The result, you can change the dynamics of your amp and how it responds to your playing in a huge way.

At first glance you see the words “Boost Gain” and “Boost Volume” and assume they are your typical master volume overdrive.....but they are not. Much like a high end boost pedal, the boost channel allows you to add “Boost” and create either clean boost or overdriven boosted gain, which is interactive with the overall gain level of the Dirty Boy’s Guitar Volume control. Sound complicated, not at all. If you play your amp at a level of gain and tone to suit your liking using only the non-boosted channel, you can now add a punch to that same tone and even control how loud that punch is with the Boost Volume. Most guitarist need that control to allow them the right amount of drive and push so they can deliver the lead that cuts through without killing the audience in the process. But if you want them to walk away with their hair straight up in the air, the boost channel is the way to do it!

Question:

So what makes the Dirty Boy so different from other amps? There are many amps in the market that offer a variety of features.

Answer:

For starters, This amp is 100% made in the USA, that means it is BUILT IN THE UNITED STATES, not off shore and packaged here. Every aspect of the Dirty Boy from the metal work, the transformers, the tube sockets, the turret boards and even the knobs are all, 100% USA built. We even use New Old Stock 12AT7 American tubes because they are BETTER then what we can buy built in China, Russia or any modern tube produced at present. The Dirty Boy is built with the trade mark high quality craftsmanship and articulation that make up the highest quality building standards Mojave™ is so well known for. Over the course of 15 months, we spent a great deal of time and effort searching for the best and offering real American built products to use for the development of the Dirty Boy amp. It is after all, a truly original American amp, not a clone of another amp product that is so pervasive these days. The Dirty Boy amp in a nut shell, is one of the most innovative products for guitar players who seek true tube amp tone that is reliable and of high quality.

If your a modern age guitarist there is definitely something in this amp for you that you cannot get from the typical high gain preamp multi-channel low cost production amp. You can get YOUR sound and not just everyone else's. The Dirty Boy cannot be bought nor can you find anything like it in a music store. It doesn't exist.

Lets look at the nuts and bolts of the Dirty Boys actual function and how it works for you, the guitar player.

Variable Power amp output from 0-100 watts of power. The Variac is responsible for the ability to vary the Dirty Boys power tube output to allow for power levels anywhere you need them. The fact that the Dirty Boy can run hot since it is a 100 watt amp and there is a bias setting to allow the tubes to run hotter then ordinary guitar amplifiers. This requires excellent ventilation. There is custom made protective front and rear grill mesh to allow easy and free flowing air flow. This is a very important design feature that Mojave™ uses on all of its tube amplifier products. Rather then using a wood front cover and relying on small vents to do the job, we know for sure your amp is well ventilated and that means better reliability and dependable operations. The tubes are also protected much better if something were to bang up against the rear back metal mesh since it is thick and strong as opposed to a thin easily bent or broken screen backing. Many amps have no screen at all. It is important to consider the safety of both the user and the product so we use heavy duty metal mesh for your benefit. The mesh protects the user from anyone touching the tubes and getting burnt or from something hitting and damaging the tubes.  The Variac itself is housed inside a metal case. This case is fasten down to the chassis and will protect the high quality STACO variac from debris getting into the contact area of the transformer.

A non-magnetic aluminum chassis is used to construct the Dirty Boy amp. This lightweight metal is thick and strong with welded seams and will not corrode or rust. The entire amplifier is housed with a Baltic Birch 11 ply head cabinet.

Question: How does the Dirty Boy keep the tubes and the rectifiers at the correct operating temperature?

Answer: The Dirty Boy uses “Auxiliary Heater Voltages” for all the tubes including the 5U4 rectifiers.  That means no matter how low you want to run your variac, your tubes are always at the correct operating temperature.

Question: Why is there a Variac in the first place?

Answer: The best way to understand the use of a variac for a guitar amp is this; when you change the power or high voltage applied to the power tubes, you are effectively changing the behavior of the amplifier and therefore changing it’s volume and tone characteristics. This means you can achieve sounds at lower power levels or lower volume levels and at the same time get even more saturation from the amp. It also means you can develop more interesting sounds and change the dynamics and behavior of the amplifier in ways you simply would not be able to do without a variac.

Question: Is the Variac safe to use? Will it damage the tubes?

Answer: Yes the variac is safe to use and it will not damage your tubes.

Question: Why are there big tube rectifiers in the Dirty Boy?

Answer: The 5U4 rectifiers are essentially the power supply for the EL34 audio power tubes. This means you get that old school tube sag that so many of the early tube rectified amps had. This also means there are behavior changes that can be had with the interaction between the variac and the tube rectifiers you cannot expect to even come close to achieving with ordinary amplifiers.

Question: Is the preamp affected by the variac and are the voltages changed when the variac is adjusted?

Answer: No, The voltages on the preamp are not effected by the variac. the Variac only effects the power tubes. The preamp tubes are fed their own separate B+ or high tension voltage. The preamp tubes are also run at a very lower gain level or lower voltage to allow for a clean non-distorted signal which is very useful when the variac is reduced in power. That means your preamp is independent of your power tubes and the tube rectifiers feeding the power tubes. The voltages feeding the preamp are constant and steady.

Question: What is the best way to use the Variac?

Answer: There is no best way, you set the variac to what sounds best to you. The possibilities are almost endless when you consider the variac is just one component of the entire amp and the interactiveness between the variac and other controls of the Dirty Boy is very cool.

Question: This sounds complicated, is the Dirty Boy hard to use:

Answer: To the contrary. You can simply plug in and play. we provide three quick start settings for you to use as a guide for clean, dirty rhythm and heavy lead tone. With these three quick start settings your on your way to killer guitar tones that will literally blow your mid.

Bias control:

The bias control is a super cool and unique feature of the Dirty Boy amp. The original Dirty Boy amp did not offer front panel user adjustable Bias or feedback. We at Mojave™ ™ Ampworks wanted to bring these features to the user for easy interactive use. the bias control is a simple control and does require some respect when using it. Here is how it works:

The bias on the amp is basically how hot your power tubes will idle. Normal idle power for a 100 watt guitar amp is typically 70% of the maximum tube plate dissipation. For a 25 watt tube, which an EL34 is, that equates to 17.5 Watts of idle. .70 X 25 watts = 17.5 watts. On the Dirty Boy, when the bias control is set to 70-75% will yield just that, a normal 70% operating idle. This is with the variac set at 100% full power. If you reduce the bias to lower then 70% your tubes will idle ‘colder” or under the 70% mark. That will mean they will get grittier and there is a point when they actually shut off the tube and you will hear nothing when the amp is on and you are not playing your guitar. This feature is extremely cool, no pun intended. The cut off effect can literally change the way you play. If you could imagine turning your guitar volume on and off so fast that everything in-between your notes is dead quiet, you would imagine the sound being very tight, and articulate. This is exactly the outcome of a extremely cold bias setting on the Dirty Boy. This means your super fast chops are now articulated even better without that crazy noisy filler that is always all over your guitar notes with the typical high gain pedal or high gain channel amp. Nothing you have ever played will feel like the cut effect. On the other hand, when you run the bias up and over the 70% range, you will be running the tubes hotter. The hottest the amp will run is 25 watts per tube or 100 watts at idle. That would scare most techs to death but not us. The Dirty Boy is safe to run at full hot bias but we suggest you take advantage of this feature for clean tones. This is the bell tone and same characteristics of a cathode biased amp in that you are running the tube very hot and they will yield greater harmonic content. So variable bias offers enormous options for you to experiment with and find your own cool sound.

Question: Isn't running your tubes cold going to produce a harsh sound?

Answer: Yes but that is not always a bad thing. You would be surprised as to how many great amps are running cold.

Question: If you run your tubes at full hot and the variac at 100% power can’t you damage your tubes:

Answer: we have tested the Dirty Boy for long periods of time to weed out the possibility of failure in this scenario. We recommend you run your amp at normal operation bias (70%) which is a safe and normal operating bias. As stated above, if you have the variac at full power or 100% and the bias at full hot, you should keep in mind this will be harder on the tubes if you are simply cranking the amp full power and pushing it into clipping. You can achieve the clipping sound with much better and safer results if you reduce your bias to under 70% or, simply reduce the variac. So long as your working with the amp in a sensible fashion, you are not at risk of damaging your tubes. We strongly recommend using the Dirty Boy for clean playing when setting bias over the 70% mark. That is its greatest asset and benefit and you will discover enormous harmonics not found on a regular amp.

Feedback control:

Here is where the amp can really give you some great options. Feedback in essence is more of a dampening function. The more feedback, the quieter the amp and the cleaner it will operate. When you reduce the feedback, the louder the amp and the more gain and touch sensitivity you will achieve. This is synonymous with the Lead vs Bass idea. Bass amps would be heavily dampened for cleaner and smoother transient response. On the other end of the spectrum, a lead amp would have a hotter higher gain and greater transient response. Both of these are very influential to your amps behavior so you can expect to find some very interesting effects. Lets say you have dialed up a killer tone but its just to dirty. Instead of changing a bunch of controls, especially the guitar volume, simply dial the feedback to increase the feedback level. That will dampen down the signal and offer you the difference you were looking for. Conversely, you might get that sound just right but with not enough gain or touch sensitivity. Instead of being locked in with one input sensitivity like a high or low input jack or instead of adding more input gain, you can simply reduce the feedback and allow the amp to act on the transients more, thereby getting you that touch sensitivity you need with a kick. Lots of cool interaction here with the adjustable feedback.

Boost Channel:

Question:

How does the Boost Channel work?

Simple. It will jack your guitar input volume or gain to a super pumped up sound if you set the boost volume up and the boost gain moderately half way. This is great for that kicked up lead tone but without the masked-over, buried in the mix character that is often the case with stomp boxes or high gain channel switching amps. To be more precise, the Boost Gain is in effect a gain control that will ultimately create clipping at a preamp level but due to the voicing, the sound is kept clear and sharp. The Boost Volume is the level of the gain control bleed out to the amp and in combination, it acts like a boost rather then an overdrive. There is a Deep switch also. The deep switch allows single coil user to get a fatter sound all together and you might want to leave the boost on for that reason, even if your not running the amp on a heavy distorted or cranked up sound. The Dirty Boy is mainly a power tube distortion amp so your preamp will serve you well if you allow it to breath and behave normal. That means instead of thinking of the Dirty Boy as a preamp overdrive and non-override amp, which it is not, you have a free flowing powered preamp section that is clean until it hits the power tubes where the rich harmonic saturation is going to color the sound like only a power pentode can do.

Power Amp input on back of amp:

This input allows you to use your favorite preamp for an input and harness the unique power section of the Dirty Boy. You can take your favorite multichannel preamp to a new level by feeding it into the Dirty Boys power amp section. By doing so you can get that crushed out sound only the Dirty Boy can offer with its unique Variac/Tube Rectified power amp section. Very cool option for experimenting.

Question: Can I get the Dirty Boy with an EFX loop?

Answer: No, the Dirty Boy is a”Power Tube” distortion amp and is not designed to accommodate EFX in the preamp section. We suggest you use a line box for line level output to derive the line level signal to feed an EFX unit live.

Question: How long will the tubes last in the Dirty Boy amp? Will I need to change them often?

Answer: The tubes will last many many years if used properly. If you have the desire to change tubes you can do so on the preamps and the 5U4s. We do not recommend you change the power tubes. You should return the Dirty Boy to the Manufacture for power tube replacements and a full check up if you decide to have the power tubes changed. See warranty information for details.

Question: What kind of tubes do you offer in the Dirty Boy?

Answer: We equip the Dirty Boy with our own specially selected and graded Ruby tube 12AX7s preamp tubes. We use an American Made 12AT7 for one of the preamp tubes. We equip the power tubes with Valve ART EL34 power tubes.

An optional power tube upgrade is available  at time of order. The upgrade is S.E.D. or otherwise known as “Winged Cs” EL34s.

Question: Can I send you my New Old Stock Tubes to install in the Dirty Boy at the time of placing the order?

Answer: Yes, We have an Aplitrex AT1000 Tube tester on hand and we will test your tubes prior to installation. If they test good we will install them and they will be put through the burn in process which is 24 hours at full 100% power at minimum bias. This is a stressful test. If they survive that burn in, they are good to go. That is the same burn in we put our own tubes through before they ship out. This will weed out any weakness if any exists in the tubes. If you send your tubes to us and have them installed, you will be responsible for them and they are not covered under the factory warranty.

Question: Do you offer New old Stock Tubes such as 12AX7s and EL34s?

Answer: Yes from time to time. Depending on stock. If this is of interest to you, you may inquire at time of purchase. Market price fluctuates with supply and will be dependent on availability.

Question: Can I use the Dirty Boy with my own speaker cabinet? If so what is the recommended impedance?

Answer: Yes, you can use the Dirty Boy with any 100 watt cabinet. The minimum impedance is 4 ohms. The Dirty Boy comes standard at 8 ohm or 4 ohm operation. You can use two 16 ohm cabinets plugged in at the same time for a total of 8 ohms but you cannot use a 16 ohm cabinet as the impedance will be mismatched and may cause flyback voltages in the output transformer.

Question: What is Flyback Voltage?

Answer: That is when to high of a voltage is developed internally in the output transformer do to improper impedance loading. This will create the capacity for extremely high voltages to develop and possibly create break down of the insolation between the wire.

Question: Why doesn’t the Dirty Boy have a 16ohm tap?

Answer: To preserve the original sonic characteristic of the output transformer we did not add any additional wiring to the output transformer. The original Dirty Boy output transformer was heavily over built and made with an 8 and 4 ohm tap only.

We offer a custom developed 4X12 cabinet that is perfectly matched for the Dirty Boy amp. Our Cabinet is set up with extra solid Low end response , extra lift in the midrange and a tapered high end to avoid the ice pick effect that can occur if not well matched with the amp and speaker cabinet.

The Dirty Boy distortion can be very much like the 300 pound Cello sound. The draw of the bow creating that rasp and rich harmonic sound but also a crazy driven tone that is laden with that warm woody characteristic which many guitar players seek out.

Check out the sound samples and settings for the sounds your hearing. These sound demos are great for gauging the sound and with the settings marked out, you will get to see how the amp sounds with the settings in their respective positions.

We want the Dirty Boy experience to be one that you will walk away with nothing less then a serious satisfaction, and you will find yourself digging deeper into the sonic pallets and varieties you can only get with the Mojave™ Ampworks Dirty Boy.

Question: Doesn’t a Variac cause tube damage?

Answer, Not in the Dirty Boy. It actually preserves the tubes.

Question: Doesn't the heater voltage need to be constant, how is that maintained if the variac is adjusted down from normal 100% operating voltage.

Answer: The variac does not provide AC power to the Heaters, nor does it provide AC power to any part of the amplifier other then the two 5U4 rectifiers which are dedicated to powering the four EL34 power tubes. This means the Variac only adjusts the high voltage on the power tubes via the 5U4 rectifier tubes.