12AX7A.COM is pleased to provide you with this free visual guide to improving your amps tone. No technician is needed for any of these improvements.
The tubes on our website are Application Graded TM so that
you can get optimized performance without spending extra money
on high-performance tubes where they would be of small benefit.
It all is quite simple when you see how it comes together in your
amp, the examples shown narrate quickly from simple amp to many-tubed
amp. When you look at the layouts, picture yourself standing behind
your amp. From right to left the tubes are designated V1, V2,
The most important tube is the one your guitar sees first (V1)
. It sets the tone and character that all the subsequent tubes
have to work with. Usually it's the tube all the way to right,
more on that when we see the models with 4 inputs. Small amps
may not have a subsequent preamp tube. Here is the Fender Champ
The guitar plugs in the top right and goes to the only preamp tube, shown in RED.
RED is signifying the importance of this tubes performance, select a tube we Application Grade TM as "GAIN".
You can see that the input jacks wires up to the GAIN tube.
Notice that there is one output tube; a single 6V6. The 5Y3 is a rectifier tube.
REPLACE ONE TUBE AND DRAMATICALLY CHANGE YOUR AMPS SOUND. Use only genuine 12AX7A Applications Graded TM tubes!
The next tube down the line also has an audible impact on the
tone, but not as pronounced: The Vibro Champ gives you another
gain stage so you can further refine your sound. Although it is
a gain stage, the amount of signal voltage gain is not
high. Therefore you can use a tube that is not the equivalent
of a race horse, and you don't need to spend that much on the
tube. Simply select a "FUNCTION" Applications Graded
TM tube. This will keep your costs down, and you won't have to
worry about the tube being microphonic.
The "FUNCTION" tube is marked in YELLOW. FUNCTION graded tubes are also available at the main page.
Next we should see when and where to use a "DRIVER"
This amp uses more than one output tube. So matched output tubes make sense, even more sense when using a "DRIVER" tube. The DRIVER tube is a rarely qualified tube in that the two triodes in the glass envelope are working at the same potential. This in turn assures that the matched output tubes have the same signal voltage to work with.
The DRIVER tube is colored in GREEN. Just to make clear: an amp with more than one output tube will benefit from a "DRIVER" tube.
Common examples of output tube types; 6L6, 6V6, 6BQ5, EL34, EL84, 5881, 6550, 7591, KT66, KT88.
The DRIVER tubes are available in all variety of sonic flavors, accuratly described on the home page. High Fidelity enthusiasts benefit from our selection of current production tube types.
Moving right along. Get ready to graduate!
The next layout shows the Fender Bassman. Typical for four
The "Bass Instrument" channel hogs up two tubes, V1 and V2.
If you are using the bass channel you will benefit from a GAIN tube in V1. Experience tells us that while a GAIN tube can be used in V2 it is not really needed and a "FUNCTION" tube will work well as a 'further refinement' tube.
Note that the 7025 tube specified is merely a 12AX7 with additional testing for low hum and low microphonics.
If you use the Bassman as a guitar amp and you use the
"Normal" channel then it is V3 that is of the most interest
to you. The "bass" channel tubes are not used when you
plug into the "normal" channel. Most people really don't
care what tubes sound like in a channel they never use, so as
long as they work, save some cash here.
Notice the 12AT7 driver tube, it can be substituted with a 12AX7 "DRIVER" for greater tonal choices. The 12AT7 has a very strong tendancy to be microphonic, and tonally is very brittle sounding, harsh. You can listen to it in the "GAIN" position if you are interested. It wont hurt your amp, but bring the volume up slowly as it almost certainly will squeal. Putting in a 12AX7 will add more gain - at higher volumes you will be able to hear the gain, at lower volumes you will be able the tonal improvement. You can read more about microphonic tubes on the ABOUT TUBES page, very helpful free information. Please visit and bookmark the 12AX7A.COM homepage.
What about an older Fender Twin?
The preamp tube layout is the same for the classic Marshall Super Lead amplifier (model 1959, others). If you have 3 preamp tubes, odds are this is the layout. Extremely common.
Note the 4 input jacks located together. This would indicate both channels are sharing V1.
I'll bet you have this all figured out. The RED indicates the GAIN graded tube is needed. The YELLOW indicated a FUNCTION tube will work just fine. The GREEN symbolizes that a DRIVER type tube is needed.
The benefits to using Application Graded TM tubes are increased tube life, better tone, better dynamics - and the ability to refine and customize you amp in a truly profound way. You can do all this at home without an amp tech, since preamp tubes are self biasing and never need any adjustment - ever. Exclusivly available at 12AX7A.com.
ANOTHER LOOK at the twin; Great Improvement, Nearly Perfected now, and MY AMP NEVER SOUNDED THIS GOOD!
More layouts below and TIPS for what to do when you don't know or aren't sure about the layout. Read on.
NOTICE: Tubes do get hot enough to scald your skin. When removing tubes you should allow time for them to cool off just as you would a light bulb. Treat the tubes extra gently when they are warm. Do not install tubes with the standby switch in the play position. Do not tinker inside the amp; you do not need to disassemble the chassis to change tubes (NO exceptions - do not go inside the amp unless you are a qualified technician). Lethal shock is possible if you avoid these simple warnings. You do not need a technician to change preamp tubes (12AX7, 7025, ECC83, 12AT7, 12AY7, 12AU7, and their substitute replacement types).
TIP; allow tubes to heat up for 13 seconds before you turn the high voltage "standby" switch to the "play" position. The tubes will last longer. It does not matter when shutting off.
TIP; If you don't know if you are replacing a tube on the channel you are plugging into then remove the tube. No harm will come to your amp. If you still get sound then the tube is not in the circuit. Skip replacing such a tube, instead consider it a spare tube holder. Do replace the tube back to its socket.
TIP; If you don't want to pull that tube then turn up one channel, turn down the other and plug your guitar in. When you tap gently on a tube with your fingernail or an eraser tip then you will be able to hear what tubes are in that channel by the presence of your tapping on the output of the amp. The tube that taps most loudly is the gain tube.
TIP; you can identify microphonic tubes by tapping them as in the above tip. Consider that since all tubes have a mechanical construction that they all possess microphonic characteristics to some degree. Microphonic tubes are problematic only if they are causing changes in the amp sound while playing. So to tell if the tone you hear when you tap is really a problem you must first be hearing something is wrong with the amp, and then you can nail down which tube it is by turning the amp up a bit and if your tapping results in a sound that sustains itself then BINGO. Substitute the tube without changing your amp settings (except power it off) and then retest.
More tips later.
I love the Fender Super Reverb!
The preamp tube layout is the same for the Fender Deluxe Reverb, and the Fender Twin Reverb.
This time we have a "Normal" channel sucking up 1 tube - V1. This channel has no reverb and no vibrato.
V2 is the "GAIN" tube for the "vibrato" channel.
V3 is driving the reverb springs.
V4 is doing two things: 1) refines the vibrato channel sound (the second gain stage for that channel) and 2) amplifies the reverb springs sound. Any amp that lets you use 2 separate tubes in the signal path offers you a creative opportunity to improve your sound. SEE NEXT TIP!
V5 is not even dealing with an audio signal! It just makes that very slow vibrato effect, and the guitar signal in no way passes through this tube. Its an excellent place to rob a tube from if you are in a pinch with a microphonic tube because a microphonic tube will work just fine here!
V6 is the "DRIVER".
TIP: Example. On refining your amps sound - for some Marshall players, some MetaL forms. You know your amp well. You play a rapid fire style that is percussive and you find the tone nice and clear but too razory in the treble zone. For the GAIN stage you will most of all need an accurate tube to articulate that speed and percussive quality without getting squishy. Then as a secondary concern you want to tame that treble, so your FUNCTION tube should sound warm.
What if you want balanced tone - dark driven beefy cream? Okay. "Warm with mild COMPRESSION and early distortion" GAIN tube, perfected with "Clean and COMPRESSED" to get the complete attitude. Rock on. Almost but not quite? Switch the 2 tubes...give another listen (you will need each tune to be Applications Graded TM for "GAIN" performance in order to swap). This is FUN!
TIP; Example. For a great clean sound start with what you think
your amp is lacking, and or what its needs more of.
Ex: I need to play louder without the amp breaking up where there is bass. I like to be loud and clean, try the "clean and accurate" tube in the gain position, and make sure you have a good working DRIVER tube (a potential source for clipping specially at louder settings). That selection of a gain tube will help to keep the bass tight and never add distortion to a clean channel. The driver needs to be a driver. Its can be anything that is not dark or easily distorted. Of course its tonal qualities further refine the amps response but not in a critical manner.
The Fender Deluxe.
The Normal channel is associated with V1.
The Vibrato channel is associated with V2.
V3 is strictly a FUNCTION tube.
V4 requires selection of a "DRIVER" tube.
The Deluxe is just a great amp.
12AX7A.com does more to help tube amp owners get what they want from the gear they already own. We have tubes that can be chosen for how they sound. Please visit.