Item #: GRO 12AT7 LIST

Groove Tube 12AT7 Preamp Amplifier Vacuum Tube

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Groove Tube 12AT7 Pre-Amp Amplifier Vacuum Tubes make your tube amp tone shine like it's new again!
Electric Guitarists both yesterday and today can be linked by one piece of equipment: The tube amp. With all the strides in transistor amp technology, guitarists still prefer tube amps. Why do tube amp designs sound and feel differently from solid-state? Simply, tubes work differently.

Preamp tubes are used in the first, low level stages of tube amps. There are many designs that will interchange and each has its own tone, gain, and response. These may be interchanged without any modification to the circuit... user friendly, so experiment!

Groove Tubes are durable and great for most US made amps, especially Fender. Use new tubes to get a cleaner brighter tone from your amp.

Note: Preamp tubes should be changed every time power tubes are replaced for best performance!

Groove Tube preamp tubes are warranted to be free of burn out, excessive noise or micro-phonics for 180 days from date of purchase.

What Is A Tube?
A tube is an electronic device consisting of a minimum of four active elements: a heater (filament), a cathode, a grid and a plate. All sealed in a vacuum glass enclosure to prevent parts from burning. Once heated, the cathode begins to emit electrons, which flow from the cathode (which is negatively charged) toward the plate (which is positively charged). The grid's purpose is to control this flow, in effect, acting as a valve.

How Do Tubes Work?
When the guitar's pickup produces a small voltage (the result of the string vibrating in the pickup's magnetic field), this signal is applied to the grid, which causes a large current flow from the cathode to the plate. Because of this, a correspondingly large voltage now appears at the plate. A portion of the amp's electronic circuitry, the grid bias control, adjusts the proper voltage setting of the grid. When the grid bias is properly set, the tube is balanced to the circuit, and therefore produces a clean, powerful signal. The plate is connected to an output transformer, which matches the impedance to that of the speaker.

How Do Tubes Distort?
As the signal emitting from the plate approaches its maximum potential, the tube gradually begins to react less and less to the original input signal. This results in a type of compression of the signal, and the signal becomes cut off or clipped. Tube distortion (clipping) occurs gradually, producing low order distortion which compliments the original signal, creating a warm sound. This is also why it's easy to move between clean and distorted tones.

Why do Tube Amps all Sound Different?
  • Types and quality of tubes vary, some tubes amplify more than others.
  • The amount of gain a tube produces varies with the each amp's circuit design, some tubes amplify more than others under similar conditions.
The 4 amp stages:
  • Preamp Stage - Amplifies an incoming guitar or mic signal for tone shaping.
  • Signal Processing Stage -This is where you add the effects, reverb, tone controls, etc.
  • Power Amp Stage -The real workers in your amp. Most amps over 10 watts use an alternating push/pull power amp design- when one tube is on, the other is off. Your amp may have two, four, six or possibly eight power tubes.
  • Rectifier Stage -Converts AC wall electricity to the DC electricity inside your amp. Most modern amps have sold state rectifiers.
Why Should You Replace Your Tubes?
Glass, metal, lots of little parts... tubes are subject to mechanical problems and are not meant to last a lifetime. Actually, the harder you work your tubes, the faster they wear out. Which means that from time to time you will need to replace your tubes. More reasons to replace your tubes:

When one starts to go, it drags the others down with it, decreasing the over all efficiency of the amp.

The better the tube, the better the tone. Simply put, the best reason to replace your tubes with Groove Tubes is that they'll make your amp sound better.

Bottom Line:
Pay attention to your amp's performance. When you hear the sound begin to deteriorate, it's time to change your tubes. Your amp will last longer. Your tone will always be at its best. Think about it, you don't wait until the strings break before you change them, do you?

Look for these signs that Your Tubes May be Deteriorating:
  • Loss of highs or lows
  • Muddy chords
  • Poor balance in the output levels of various notes
  • Lacks punch
  • Makes funny noises
  • Amp starts sounding weak
  • Power fading up and down
  • No sustain, or fast decay
The Groove Tubes Process - Step by Step Testing and Selecting Tubes
Groove Tubes literally goes through thousands of tubes, rejecting more tubes than they accept. They put every tube through a rigorous performance test, one at a time, in real amp circuits. The preamp tubes are rejected for adverse microphonics, low output or high noise. Power tubes are more involved, and they go through additional testing.

Here's What They're Looking For:
  • Grid Leakage. Causes tube to burn out quickly, and worse yet, to short out and wreak lots of havoc. They throw these tubes out.
  • Weak Vacuum. Tube will act deceptively normal, then just burn out on you (usually at the worst time!). These tubes don't make it past the first round.
  • Gain to Distortion Ratio. The center of all Groove Tube magic! This measurement tells us if the tube will distort early or later in its power range. Since the tube distortion is rich in harmonics (That's why we love 'em!), the tonality of each tube will vary according to this ratio. Only Groove Tubes sets have been measured and matched to insure longer sustain, wider frequency response and a more musical amplifier!
Rating and Matching Tubes
Groove Tubes translates this gain to distortion ratio into a performance scale that can range up to 100 points, then match up the tubes to within 1 point of each other. To simplify things, they reduce the scale to 1-10 before the tubes leave their shop. All tubes are exactly matched into duets, quartets, sextets and even octets.

More than just Great Tone
The Groove Tubes Process produces many welcomed improvements:
  • Dramatically Improved Sustain by eliminating phase cancellation (which occurs when dissimilar tones coming from unmatched tubes are combined and cancel out certain frequencies.)
  • Improved Harmonic Balance- All the notes you play will have the same amplitude. (No more dead spots or dull notes!)
  • Longer Life Span by 1st) eliminating faulty tubes. 2nd) Their balanced sets reduce stress that occurs when a stronger tube is working too hard to make up for its weaker partner, and 3rd) because their sets drive the output transformer evenly it actually runs cooler!
Groove Tubes: It all Comes Down to Tone
When you go into a store and buy other tubes, it's a crapshoot. Without The Groove Tube Process, there's absolutely no way of predicting how a tube will sound. When other tube suppliers claim to have matched sets, they're referring to the meaningless measurement of the tube's power. As we learned in the beginning, it's a waste of time to measure power because you simply can't hear variations of power (unlike variations in harmonic distortion). And even if you could, the power measurement is always changing as the tube wears (This measurement wouldn't stay matched anyway, but theirs do!). Buying Groove Tubes will save you money and a great deal of aggravation, while turning you on to the best tone you're ever heard coming out of your amp! Groove Tubes are more expensive than most other tubes. Now you know why.

The Tube-Tone Phenomenon. The next time you're experimenting with your tone, and before you shell out more bucks on effects, gadgets, guitars, another amp! ... check your amp head and try out a new set of Groove Tubes.
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Phone:  Warranty:  6 Months Preamp Tubes; 3 Months Power Tubes

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