The 2101 uses two 12AX7 tubes in its preamp for 3 different tube tones: Saturated Tube, Distorted Tube, and Clean Tube. In addition, the 2101 offers 3 other Distortion tones which do NOT use the tubes: Overdrive, Heavy Sustain, and Grunge.

Tube Refresher Course:

Tubes are early versions of today's transistors. They operate essentially the same, the only difference being the means by which they conduct current. Basically, a tube consists of 3 parts (at least): the heater (or filament), the cathode, and the plate. The overall glass tube is merely a way of keeping air out so the filament doesn't burn up. A tube made of only these three parts would be called a diode ("di" meaning two terminals, the cathode and plate - the heater doesn't count as an electrically interesting part of the tube).

Diodes aren't very interesting. They are either on or off basically, and this can't be controlled by a circuit - it's a matter of whether it is placed in the forward or reverse direction when the circuit is made. However, if we add a third terminal to the diode (a 4th component), the grid, we have something. It 's called a triode (three interesting active terminals), much like a transistor. The voltage applied to the grid causes the stream of electrons being emited from the heated cathode (the cathode is heated by the heat emitted from the filament, and, in turn, its electrons acquire so much energy they are able to leave their atomic orbits) to be rejected back towards the cathode, or to pass (even to be acceletered) to the plate. By controling this voltage at the grid, we can control the electron current flowing out of the plate of the triode. Since the current at the plate is higher than the signal at the gate, we have amplification (known as transconductance, because the voltage at the gate was changed into a current at the plate). Typically triodes are used in preamplifiers.

Forget about tetrodes -4 terminal tubes - they aren't very useful to us musicians for reasons I won't get into.

Pentodes (5 terminal tubes) take this grid thing to a higher degree. Employing three grids, pentodes overcome some limitations of triodes. Remember, the grid voltage in a triode can actually accelerate the electrons towards the plate. Sometimes they hit the plate so hard they bounce off like bullets. This causes electrons in the plate to go flying off the plate along with the ricocheting electrons, which is called secondary emmision. This causes the plate current to decrease after we increase the grid voltage beyond a certain point. Basically, this is an annoying reality of triodes. The additional screens or grids in the pentode slow the electrons back down to a reasonable speed before smacking into the plate so that secondary emmision will not occur and gain remains even. Typically Pentodes are used in power amplifiers.

What Kind of Tubes Do I Have?

All 2101's are outfitted with two 12AX7 dual-triodes. Dual-triodes means that each tube actually contains 2 triode elements, which is like having two tubes in one! Therefore, even though you only have 2 tubes, you actually have 4 triodes. 12AX7s are a type of tube (triode) used for high gain audio applications. The designation 12 refers to the heater voltage of 12.6 volts. The AX refers to the gain and application of the tube. There is a sister tube to the 12AX7 known as the 12AX7a which I will mention in the microphonics section.

Typically, these will be Penta brand 12AX7 tubes, which are made in China. If you own a GSP-2101LE then you will have Groove Tubes instead.

Note that the two tubes are labeled on the circuit board as V1 and V2. If you choose to try to get a more sparkling clean tube sound, you will need to replace tube V1, as it is the first tube, and the tube responsible for CleanTube circuitry. The second tube, V2 is employed in the Saurated and Distorted tube distortions for additional in-your-face gain. This tube should be chosen for its high gain distortion characteristics. In any case, always use 12AX7 or 12AX7a tubes to ensure proper biasing,current draw, etc.

What are the differences in different tubes?

Other types of tubes, 12AT7, 12AY7, and 12AU7 can be used for audio amplification applications, but lack the gain of the 12AX7 to distort and saturate like guitarists want. However, they do offer their own flavor for lower gain distortion and in clean tube "warmth" applications. Typically, you will see 12AY7s or 12AT7s as low gain stages in preamp circuits of tube heads and tube power amps. Studio gear such as the 2101 do not employ these extra tubes for cost reasons associated with tube designs.

Additionally, many manufacturers produce the 12AX7 tube. Each manufacturer will generate 12AX7s with slightly different physical properties (called process parameters) that will vary, causing the electrical properties to vary slightly. Some people swear by certain brands, while others couldn't care less. Realistically speaking, it is unlikely that anyone in the audience could tell a difference, perhaps even if you played a Penta vs a Groove Tube in a side-by-side "Pepsi Challenge" tube flavor test. However, your ear may discern some subtle difference which you prefer, which, in turn, may make you more confident in your playing. It's your money. If you want to try some other tubes out, go for it. They'll set ya back about $10 or $20 US.

Do I Need Matched Tubes?

No, not really. Matched tubes are simply tubes which have been tested and packaged together based upon the fact that they have very similar characteristics. Typically, an engineer is concerned about matching for the purposes of knowing that the bias point of one tube, if used for the other tube will create precisely the same operating conditions. This is important for measurement and instrumentation devices, not so much for the amplification schemes that tube preamps perform where the biasing is almost always controled by a resistor between the cathode and ground.

More importantly, matched tubes are used for POWER AMPLIFIER circuits where push-pull designs are employed. This is a design that uses a tube circuit for the positive half of the waveform, and an identical circuit for the negative half of the waveform. If there are differences in the 2 circuits, the positive and negative halves won't be symetric. Therefore, for optimum hi-fidelity, matched tubes are used. In reality, if these tubes were not matched, irregularities could cause the circuit to malfunction, or even damage itself due to the push-pull nature of its operation.

Why then does the GSP-2101LE utilize matched Groove Tubes? I have no idea. I would guess though, that it is for the same reason that people pay twice as much for some contact lenses; they think they are getting a higher quality product,or something that they need, but don't understand why, and are willing to pay a bit more for it. Sometimes people hear a buzzword like "matched tubes", and they go up to a salesman and say "I gotta have matched tubes man!" Personally, I'm sometimes amazed we ever invented the wheel.

This isn't to say that matched tubes won't sound different, just that what you want is distortion. I would tend to think that matched tubes would tend to generate essentially the same sets of harmonics at about the say levels for a given source. However, the source differs from one tube to the next since they are chained together. Therefore, the matching doesn't really come into play. I'm sure someone out there disagrees.

However, if you don't beleive ME, then take Randy's word for it (the following is a direct quote from Randy Thorderson from Digitech):

Q:  Can anybody give me a reasonable engineering explanation for why Matched Groove Tubes were used for LEs as opposed to non-matched?

A:  No...because their isn't one...I can give you the marketing reason...there is a misconception that PreAmps like to see matching tubes, when the fact is PreAmps don't care (Tube AMPS do care...totally different gig). We are learning that re-educating the customer over things that don't matter is a waste of time...so if they want matching? They get matching......It certainly doesn't hurt to have them matching...

What does "going microphonic" mean?

When you tap on a tube, the glass vibrates. To some extent, this is transmitted to other parts of the tube, such as the grid. When the grid vibrates, it actually moves back and forth fairly fast, causing the voltage charge on the grid to move back and forth in space with it. This oscillation will afect the electrons passing through the grid to the plate, and, in turn will cause the plate current to oscillate with the grid to some degree. Now, imagine you are really cranking. The sound vibrates the tube, the tube vibrates the grid, the plate current oscillates with precisely the same waveform that you just played a millisecond ago! Now you are feeding back worse than Jimi at Woodstock. This is a microphonic tube; a tube that picks up sounds/vibrations and transmits them to its output.

To determine if a tube is microphonic, yell at it really loud. No, I'm just kidding. Actually, take a pencil and tap on it with the eraser end while the tube circuit is operating. If you hear the tapping from your speakers, then it is microphonic. Realize that caution should be headed to when testing tubes since they can utilize high voltage circuits (read ZAP!).

12AX7A tubes are 12AX7 tubes that have improved microphonic resistance.

What kind of Voltage are we talking about?

Different tubes use different voltage ranges for their operation. We will only discuss 12AX7s here.

The filament (heater) needs precisely 12.6 volts. Too much more and it burns out like a bad light bulb. Too little and it won't spew the cathode's electrons toward the plate (thus, no amplification, no sound, no nothing). The plate, however, must be connected to a positive source to draw the electrons through the cathode. This source voltage can be quite high, as much as 250 volts. Sometimes you will see adds that mention "taking advantage of the tube's full 250 volt operating range". This is what they are talking about. Whether this biasing point really makes the tube sound better, distort smoother/harsher, etc is academic. I have seen schematics that use 12V, 45V, and 250V.

The following is quoted from Wayne Moss, an engineer for the 2101 (as taken by Randy Thorderson on Nov 8 1995):

"Rest assured, the tubes in the GSP2101 are not 'underpowered'. The Voltage on the first two plates (used for the Clean Tube voicing) is 192 VDC. The Second two plates (used along with the first two for distorted and saturated voices) is 141 VDC. The Peavey TubeFex uses 160 to 175 volts (NOT 250v as their ad implies) on their plates, and the ADA MP1 used 112 to 126 Volts.

"In very general terms, higher plate voltages yield more headroom and a more aggressive, 'jagged' distortion, while lower plate voltages give a more 'compressed' and 'rounded' tone. A common misconception is that equal plate voltages yield equal tones, but this neglects the fact that the plate voltage is a strong function of the DC Bias current, plate load resistor and cathode resistors. This means that two 12AX7 triodes could both have 150 VDC on their plates, but could sound and feel very different from each other because very different DC bias currents, plate resistors, and cathode resistors.

"The moral: tube preamp plate voltages can be a very general guide in evaluating a preamp, but the true measuring tools of tube tone are your ears and fingers, not the voltmeter."

(Randy:) There you have it kiddies...any questions?

Will my tube gain settings match other people's?

Probably, but not necessarily. Different manufacturers, and in fact different lots or manufacturing runs, will produce different tubes. The hardwired bias points for the 12AX7s in the 2101 will produce different currents and gain factors (gm=transconductance) in the tubes. Hence, the tubes will distort at somewhat different gain settings (which I presume are simply preamplified gains to the guitar signal at the grid). This is exaggerated by multi-stage settups such as the Sat. & Dist. tube distortions where additional variations in the gain factors (gm) will multiply with one another causing the point of onset of harsh distortion to occur at slightly different gain settings. No big deal though (in fact most differences should be indiscernable). Just keep in mind that someone else's patch may need a boost or cut in tube gain here or there.

Other user's tube experiences:

SRC Jan 1998:
i just replaced the v1 socket with some phillips 12ax7's and put a gt 7025
in the v2..i have not changed my tubes in almost three years....
that is the truth..the processor is so good that even with old stock pentas
i could mess with the gains and get a good sound...(of course i have a USA
kramer with a jeff beck pickup...) but when i changed tubes i was totally
amazed ..the friend in my band that plays guitar has a mesa boogie head and
cab with an ESP guitar with a jeff beck pickup....its brand new.... he was blown
away at my sound...and so was i ..

Tom Owens 4/5/1997: 

I now have two Phillips 12AX7WAs in my GSP. There are probably better selections of Phillips tubes I could have used (and I may look a little further) but that's what I ended up with.

For those of you uninterested in yet another tube testimonial, just delete this message and move on...

For those of you who ARE interested, here's how I ended up with them:

A month or so ago, I bought a Sovtek 12AX7WA and stuck it in the V2 socket. I bought it because I happened to be somewhere that sold them and wanted to try one so I bought it. I was already thinking I wanted to try a Sovtek 12AX7WB but settled for the WA on a whim. I liked it WAY better than the original Penta so I left it in.

I had an opportunity to buy some overpriced Phillips tubes so I did. I got a couple 12AX7s and a couple 12AT7s because someone else had testified that they liked the characteristics of the ATs and it sounded like something I might be interested in.

I set up my GSP with my Ampulator in the FX loop. Since the Ampulator uses a 12AX7, I probably got some extra tube coloration but decided to ignore that for now. I rationalized that I'm using the Ampulator as "my amp" so I might as well just live with the consequences. I can play tube games with the Ampulator later.

I tested the four different tube types I was using (the original stock Pentas, Sovtek 12AX7WAs, Phillips 12AX7WAs, and Phillips 12AT7WCs) in the V1 socket first. I used a custom patch I use a lot that uses the "Clean Tube" distortion type (and thus uses only ONE tube in V1). I set the EQ flat and used my newly purchased Gibson 175 because it will probably be my main axe from here on out. I used the ultra-bassy neck pickup. I came up with a simple 15 second musical phrase that included a big fat low jazz chord and some single notes up around the 12th fret. I played this sample four times with a different tube in the GSP each time and taped it. I played the tape back and fussed around a little more. I had Gain1 set to max, by the way.

I then put my desired Phillips 12AX7 tube in V1 and did some brief testing with V2. I pulled up another custom patch that I use a lot that uses the "Saturated Tube" type. I probably should have tested with "Distorted Tube" as well but didn't want to spend my life testing. I used the tail pickup for this test because I tend to favor the tail pickup with heavy distortion.

I came up with a short phrase and played THAT four times each. I set it up so the expression pedal control both Gain1 and Gain2 and covered the range of 4.0 to 11.0. I taped all those and listened. I got an idea of the differences and then just played around with them a little to see which was more "fun."

I settled in on two Phillips 12AX7WAs.

In general, here are my general thoughts on the differences between the tubes I tested:

Stock Pentas: These tubes have a nice low-endy quality that none of the others had but the distortion (even in V1) was "trashy." These tubes break up really easily and have a lot of that hissing, raspy, "buzzing" quality that makes it impossible to play chords and be able to tell what the chord is. I wish I could get the low-end quality out of the other tubes but the trashiness made them my least likely candidates... except for the ATs. More on the ATs later.

Sovtek 12AX7WA: The "quality" of the distortion from these tubes was DAMN close to the Phillips. But the output levels between Gain2 4.0 and 11.0 was quite dramatic. That surprised me. The guys who wanted the "Clean Tube" sensitivity from the "Saturated Tube" setting might want to take these for a test drive. The Phillips seem to compress the signal more. The Sovtek may end up in my Ampulator. I lost the low-end quality of the Pentas but I also lost the trashiness. I can live without the low-end in favor of ditching that trashy sound.

Phillips 12AX7WA: No trashiness. A little bit better low end than the Sovteks (especially evident in V2). These guys fit into the sockets REALLY tight. That was one of those ultra-practical aspects I liked; it doesn't affect the sound but it IS a plus. I would have preferred the wide dynamic range that the Sovteks had but having that little bit of low-end tipped me back in favor of the Phillips. That and the tight fit. I rationalized that the more compressed signal in V2 will be easier to control in a live situation, so that put the Sovtek out of the running. This is my present tube of choice.

Phillips 12AT7WC: These are neat in that you can stick them into V1 and crank the gain ALL the way with almost no distortion of the signal... Assuming that's what you want. The best word I have to describe them is "brittle." Someone else used that term recently and I didn't know what it meant. Now I do. In both V1 and V2 sockets the AT made the GSP sound like a Fender Twin. I always hated my Twin. In *so* many situations with my Twin, I wanted more "oomph" that just wasn't there. The ATs made me feel the same way - something missing... These tubes are obviously not the tube for me. They behave with phenomenal sensitivity in the V2 socket. With Gain2 at 4.0, there's very little breakup. At 11.0, they behave like the AX's except I don't like the tone. If I had an AT in socket V1, there probably would have been no distortion at all with both gains set to 4.0. I lost the Penta low-end with these as well. They sound thin. Like a Twin. Ick.

Kevin Kennedy (Kennedy Audio Labs) 3/5/1997:
I think some of you audiophiles may be interested in the admittedly subjective results of some listening tests I recently performed on a variety of 12AX7's and their clones.

Two amplifiers were chosen for the evaluation, both of which use 12AX7 type dual triodes in their input circuitry. Both are loosely based on the Dynaco ST-70 and one features triode circuitry thruout. The amplifiers chosen were the PAD ST-70 with ultra-linear outputs and the Kennedy Audio ST-70T, a short description of each is provided in the following paragraphs.

The Purist Audio Design (PAD) is a elegantly simple design utilizing a single 12AX7 per channel as a cathode coupled (differential) phase inverter with no negative feedback - loop or current in the voltage amplifier stages. This amplifier is well suited to this application since all of the colorations and distortion products are audible due to the absence of loop feedback, output linearity is good due to use of a limited amount of current feedback in the cathode circuits of the output tubes. Tube generated hum and noise are very audible in this amplifier, assisting in determining the overall quality of the tube. Overall performance of this amplifier is excellent into my AR-58S loudspeakers.

The Kennedy Audio Amplifier ST-70T (KA) utilizes a single 12AX7 voltage amplifier shared between channels driving a pair of cathode coupled 12AU7A's which in turn drive the respective pairs of output tubes. Open loop gain is high enough to allow for up to a 20 dB feedback margin depending on selected output mode. Local current feedback is employed in all stages to enhance linearity and to allow for precise control of overall loop gain and bandwidth. Overall design philosophy means to optomize circuit performance in the face of varying tube parameters. This amplifier will drive difficult loads with ease and is relatively unaffected by variations in load impedance. Overall it has a slightly different sonic character than the PAD, and overall speed and linearity are better. Slew induced distortions caused by inferior tubes are quite audible when present.

The testing was performed under relatively uncontrolled conditions, with a very limited sample size and with only two amplifier designs, even so the information should prove useful in a lot of cases. Source material was mostly CD with a smattering of analog source material. (CD's - Dave Grusin's Baker Boys album, Charlie Brown, Harmonia Mundi's Tarantula, as well as the Stereophile test CD among others, LP's were Lars Erstrand and Brothers Four on Opus 3, Respighi's Pines/Fountains of Rome on Chesky.) The CD player is a heavily modified 14 bit Philips, the turntable an AR with a modified Mayware arm, the cartridge a modified Shure V-15, the pre-amp. is one of my designs utilizing passive equalization, and no over all loop feedback. Speaker cables are Apature Signature 500, and interconnects are various home brew items... (I know that this is far from the ultimate - but wait until I'm making a little more money....)

Please bear in mind that the rankings are really only scientifically meaningful in the context of the specific electronics used, but that gross deviations from best to worst will probably be audible in most tube equipment presently used. Usual disclaimer: I don't have any connection with any tube vendors, or manufacturers, and furnish tubes only as a courtesy to my customers. The following is a ranking of tubes based on my sonic preferences in the two above amplifiers, from best to worst:

1.) Tungsram ECC83/12AX7A (Hungary) Substantially superior in the KA and PAD amplifiers, very quiet, clean and detailed. Superiority particularly pronounced in the KA amplifier where its low distortion and high resolution were very obvious to all listeners. Detail present that was lost with all other tubes, excellent sound stage, lots of "air" between instruments, excellent harmonic structure, very neutral and cleaner sounding subjectively than all others.

2.) Philips ECG 12AX7WA/7025 and Sylvania 12AX7A (USA) Slight hum and hiss audible in PAD, dead silent in KA, very detailed, clean, transparent, quick. Very good harmonic structure, and "air" between instruments, excellent sound stage. Fairly neutral sounding in KA. Good bass extension in both amplifiers. Considerable loss of resolution as compared to the Tungsram tube above. RCA 6681/12AX7A (USA) Evaluated only in the ST-70T, this tube is an enigma, not particularly well known, if its performance in the KA amplifier is an indication, it is worth another look. It easily outperformed the Sylvania 12AX7A. Very clean, excellent harmonic structure, inner detail, sound stage and depth, freedom from overload effects under all conditions, quick, open, lucid mid-range, extended well controlled bass, accurate treble under duress. I would rate this tube as better than the Sylvania, but limited experience prevents me stating this to be the case under any other conditions...

3.) GE/Sylvania 5751 (USA) Slightly quieter than the Philips in the PAD amplifier, dead silent in the KA amplifier, very detailed, slightly forward balance in both amplifiers. Quick and clean, detailed, lively, otherwise very similar to Philips ECG above. Frequently outperforms 12AX7's in pre-amplifier circuitry.

4.) Brimar 12AX7WA/CV492 (Britain) Slightly noisier than any of the above tubes in the PAD amplifier, very quiet in the KA, good detail, fairly neutral timbral balance in both amplifiers, clean, good bass extension. Good sound stage depth, very pleasant without being euphonic, more neutral than 5751. Less noise would have put it in the number 3 position... Excellent overall.

5.) Mullard CV492/12AX7MC (Britain) Relatively quiet, some hum evident in PAD, dead silent in KA. Clean, neutral timbral balance, good inner detail and sound stage. Good bass extension. Agressive, yet controlled presentation with excellent harmonic detail and attack characteristics, dynamic with no sense of strain in the KA amplifier. Very similar to the Brimar and highly recommended.

6.) AR 12AX7B (India) Very quiet, slight hum in PAD, not tested in KA, very solid well controlled bass response, slight thickening of texture in the mid-range and some brashness in the treble, good timbral balance, slight loss of detail, overall very good.

7.) India ECC83 Allegrosound (India) Structurally identical to the AR, and "Allegrosound Frosted", very quiet, slight hum in PAD, silent in the KA. Clean, well balanced sound, some thickening of texture in mid-range, slight brashness in the treble. Good harmonic detail, somewhat lacking in depth, with some high frequency distress on crescendo's in the KA amplifier. These Indian tubes are very similar overall, but the AR is selected for low noise. Good.

8.) Allegrosound 12AX7A Frosted glass envelope (Indian manufacture) Significantly noisier than any of the above, substantial hum in PAD, quiet in the KA. Very solid bass response, well controlled, slight "chestiness" in mid-range, slightly brittle treble, good detail in the PAD. Not so great in the KA amplifier, additional distress on high frequency crescendo's and loss of harmonic detail are quite evident. Not too bad, it seems to be a better match in inherently slew limited applications.

9.) EI 12AX7A/ECC83 Penta, National, Procomm, etc. (Yugoslavia) Fairly noisy and moderately high level of hum evident in the PAD, fairly quiet in the KA. Substantial loss of detail in both amplifiers, thick almost syrupy mid-range and soft, sweet treble. Bass extension is ok, but loss of control is evident to some extent in both amplifiers. This tube is good in the PAS-3 however..... Quite inexpensive, but barely acceptible in some applications and good in others. This is the same tube that some vendors sell for $25.00 each and up - not worth the expense in my opinion, they sound no better than the $2.95 version of the tube.... Not recommended, except to those on a serious budget, or PAS-3 owners.

10.) Shuguang 12AX7A @#**?!?@#!!!! (Chinese) Very quiet, some hum audible in PAD - one of the quietest tubes of the lot.... Too bad it doesn't sound better. Rough, edgy almost shrill sound quality in the treble regions, very dry, antiseptic mid-range, lack of harmonic detail, shallow sound stage, bottom end lacking in punch in both amplifiers. Fairly poor sound, but very consistent and reliable. These don't sound very good in most pre- amplifiers either... Not recommended. (Strangely enough some early samples from around 1983 seem to sound better!?)

Suki 3/4/1997:
I have a higher gain tube (Sovtek 12AX7WB) in V1 and regular gain (Philips 12AX7B) in V2. Why? Even though the Philips sound better overall (more clarity and full range sounding), the higher output from the WB's gave a bigger, fuller distorted sound. Probably, because the higher gain makes the second tube clip harder. Also, on the Clean Tube setting, the Philips didn't distort too much. But the WB's do and to me it gives a nice overdriven tone. I can still back off on the gain to give me a spanking clean tone. In the end, I gave up a bit of clarity, for more tonal variety. I don't think I sacrificed much though. I'm not helping in the way of clearing up the confusion, but it depends on what you want, I suppose.
Paul Comi 3/4/1997:
I found a source for Philips 12AT7 today after calling New Sensor in NY. I took my tubes home feeling so special and proud expecting to find Nirvana in a tube, but instead I found that the old GE12AT7 that I pulled out of my old Fender amp sounded better. When I played anything using clean distortion I found that the low strings had more punch and the overall sound was fatter and more satisfying.

I begged the guy to exchange them for GE12AT7 JAN tubes and I love my sound. I don't know what sound you guys are going for, but for me I am much happier (thanks to earlier feedback from others-I would never have thought to use 12AT7 in both positions).

With a GE in v2, I find that the distortion and saturated distortion sounds really healthy-but if you are a satriani freak, you may not want it because it doesn't have that state of the art modern distortion. For me, I prefer the kind of distortion that you would hear on old Van Halen albums and my telecaster through my rig totally rocks now. My biggest challenge is to get a sound that allows me to vary the amount of bite my amp gives depending on how hard I play the guitar. With the GE tubes in both positions it just feels the best to me. My advice to the people who like the Philips-check out the GE's. I think you'll be happier with them.

Tom Owens 3/3/1997:
I just now replaced the Penta in my V2 slot with a Sovtek 12AX7WA. Left V1 stock. I'm VERY pleased with the results! I picked a distorted patch I've been using a lot lately, set Distortion to Saturated Tube, cranked Gain 2 to 11.0, and REALLY liked what I was hearing.

Stuff that sounded like a hissing cat before now sounds like a pleasantly distorted guitar. A Barre Chord on the fifth fret still sounds like a major chord. Simple melodic lines in 3rds sound GOOD... With gain set to max!

I still want to try some other tubes but this first test yielded some mighty fine results. There have been a couple people who claim new tubes didn't make a difference. In MY case, it made a BIG difference. Just thought y'all should know.

Paul Comi 3/3/1997:
I tried a 12AT7 in V1 was really impressed with the improvement over a Sovtek or stock tube 12AX7 in the same position. It has a lot better bottom and doesn't sound so rough. Its closer to the sound I love of an old Fender with no master volume cranked up-your basic late 60's surf. I tried several 12AT7 tubes in that position and came to settle on one which was unmarked and I wonder if someone knows what it is. The markings on it are 12AT7 ECC81 and also on the tube in smaller letters mz 188-5. It sounds similar to an old GE that I pulled out of a Fender Super Twin, but was microphonic when cranked up to 11.I wonder if the Philips will sound better than this one. Also, I am now using a Groove Tubes 12AX7 in V2 which after trying a Sovtek 12AX7wxt and a Sovtek 12AX7wb gave me a better sounding distortion. I am considering a Philips in v2 also. Any thoughts?
James Thomas 3/3/1997:
I changed swapped my valves (sorry, "tubes") to 12AT7WC's, but they weren't Phillips or Sovtek, they were by some manufacturer I've never heard of. (Zearix?? - I think they are well out of business by now). They sound awsome, a massive improvement over the Penta 12AX7's. It should be noted that the 12AT7WC's are Mil-Spec. though.

It just makes me wonder if it's actually the manufacturer of the tubes that really matters, or just the type of tubes they are. How many people wrote to this list saying 'I changed to [Sovtek, Groovetube, whatever..] and noticed no real audible difference??

I've got 12AT7WC's in both slots now. It sounds like a new rig...

Thomas van Beek 2/3/1997:
I tried an ECC81 (Philips) for distorsion but it lacks gain and sounds thin.

I tried various other tubes (different brands en types of 12AX7) and found that for me the Philips ECC83 sounds better than the original Penta's. But the tubes that I liked best are: Telefunken ECC803 (military type) for clean and Telefunken ECC83 for distorsion. The distorsion is less aggresive (bluesier). Unfortunately I didn't have the Sovtek tubes to compare with so I still have to compare them to the Telefunkens. I like Philips but I think they are second best as compared to Telefunken (unfortunately because I have bought a number of Philips ECC 83's in the past for repairwork).

Nick Roznak ([email protected]) 1/14/97:
I have an LE with the original GT's and am happy with the sound most of the time. But I have my rig set a little different. I don't use the GSP compressor or noise gate for distorted sounds.
Brian Hansen ([email protected]) 1/14/97:
According to what I've read as well as what my local dealer is saying, Sovtek rates their tubes like this.
12AX7WA low gain low noise

12AX7WB a little higher gain, smooth milkier like sound, and low noise.

12AX7WXT high gain, but more harsh and brittle sounding.

12AX7WXT+ Even higher gain, and supposed to be warmer. (more like the Chinese 12AX7.)

Groove Tube rates their tubes like this.
12AX7A This is a Chinese 12AX7, and according to what the people at GT have told me this is the one they suggest for the 2101.

12AX7R This is a Russian 12AX7, and again according to the GT people they claim this tube has a harsher distortion and is not quite as warm sounding.

I'm quite satisfied with my GT's in my 2101.
Mike([email protected]) 12/12/96:
I just switched from Groove Tubes to Sovek 12AX7WB's (B's are the middle of 3 Sovtek 12AX7's, A's are "quiet" with lower gain, and I forget the designation of the higher gain tube).

For a bluesy type, vintage Fender cranked amp "type" of sound, these kill the Groove Tubes I was using. I'm considering getting an "A" for the clean tube position.

If you're after radical distortion though, stick with Groove Tubes.

Dutch VanZile ([email protected]) 12/6/1996:
I have had very good results using two different 12AX7 types: I have found that the current-manufacture Philips 12AX7 to be excellent for clean and lightly distorted stages. This tube is manufactured with tooling that Philips bought from Telefunken, and the tubes are virtually identical to the most recent smooth-plate Telefunkens in every respect except the lack of a diamond shape embossed in the glass between the pins. For distorted sounds, Sovtek's 12AX7WB works exceptionally well. It reacts well to being pounded with a hot signal and gives a very smooth, harmonically rich overdriven and saturated tone. I would recommend a Philips in the "clean tube" slot, and the Sovtek in the later stages of the "dirty" and "saturated" circuits. Philips 12AX7s can be bought at Antique Electronic Supply in Tempe AZ. Their phone number is (602) 820-5411. They are a good source for many different tube types, and their prices are fairly competitive. They are probably also available through Mojo Music and New Sensor, but I haven't checked, since I live about 6 miles from AES....
Chris Bleill ([email protected]) 10/22/96:
I just replaced both of my tube with Groove Tubes and really like the sound over the Pentas that were stock. The Groove Tube in the first position stays cleaner at higher gain with the "Clean Tube" setting, and gives me more than enough gain on the "Saturated Tube" setting. They really agree with my Strat. I highly recommend switching to Grove Tubes.

Perry Baker ([email protected]) 10/12/96:
"A few weeks ago I wondered out loud what replacing one or both of the preamp tubes with something a bit more low gain would sound like.{Cries of outrage. Perry, have you lost your mind? You know everyone in this group wants more gain. Not less.} I tend to use heavy distortion infrequently, so I didn't think the loss of some gain would bother me much. An old tube manual I have, said that replacing a 12AX7 with a 12AT7, or even 12AU7, is O.K. in a pinch and since Randy remained quiet when I asked about the dangers of such a swap (I know he couldn't give a thumbs up go ahead, but I'm sure he would have responded quickly if there was going to be a problem). I tried the swap last night. I only have one 12AT7, so I've only tried it in one position so far.

The results: With the 12AT7 in the first position, the CLEAN TUBE settings sounded more... (I hate trying to discribe sounds)... I want to say "Hi-Fi". Not like using a DI, but maybe more like Jerry Garcia, if you know what I mean. Cranking the gain up to 11 adds more warmth. No noticeable distortion. More like Al DiMeola's clean sound. It just gets nice and round, kinda like an old Magnatone amp I've got that I used to use for jazz. The DISTORTED TUBE settings were a little "darker" than before. Great woman tone at 11,7 with my PRS, but I don't much care for what it does to my Rickenbacker 12 string. It seems to have less of that ringy sound. Maybe if I play with the EQ's a bit more I can find it in there again. The SATURATED TUBE sounds darker too, and of course nowhere near as much gain as before.

I need to experiment a bit more to decide if I really want to keep this tube in there. All of my gain and EQ settings need to be readjusted. I like what it does to my PRS, but I haven't found a tone that I'm happy with for my Ricky yet and although I haven't tried it with my Gretsch, I suspect I will find it too dark for that guitar too."

Tom Hespos ([email protected]) 9/30/96:
"I finally got around to replacing my stock tubes with Groove Tubes. Actually, my tech did - I am still afraid I'm going to blow something up, so I took it to my dealer. Didn't seem too complicated - I watched him do the whole thing standing on one of those static mats with a grounding bracelet.

Anyway, these tubes really fattened up my sound. The distortion tones sound, well... ballsier. (Sorry if I'm offending anyone, but I couldn't find a better word.) One thing that happened that I didn't expect is that the clean tones sounded "ringier." There was clearly more of a "bell-like" tone, with better sustain.

I was perfectly happy with the Penta stock tubes, but after hearing from my tech that his ADA preamp sounded 100% better with Groove Tubes, I had to at least give it a shot. I would recommend switching tubes to any players out there who want a fuller distortion tone with more "edge." Definitely makes the clean sounds better, too, IMHO.

One other thing - I have this off-the-wall patch that cranks the distortion through the roof. Once I put in the new tubes, it sounded a little overboard, so I lowered the distortion gains a little bit. All is okay, now. This custom patch was the only one I had to attenuate - all the others, including the factory patches, seemed okay."

Larry ([email protected]) 9/28/96:
Q (Curtis Pastor): "[talking about replacing 12AX7 tubes with lower gain 12AT7 tubes in the 2101, and any possible consequences]...I really didn't think it would hurt anything since the voltage levels are the same (12xx7). How did it sound? I would imagine the 12AT7 or AU7 might actually be sweeter than the 12AX7 -- am I deluding myself?? Could you notice any distinct benefit/loss besides gain (maybe even the way it broke up when it started to distort) that you liked/hated?"

A (Larry): "I tried a set of 12AT7's in my 2101. It made the tone more dynamic and lively. However, I couldn't get the "over the top" tube distortion that I could with the 12AX7's, and the clean tube settings barely broke up at all. It might work if you put a distortion pedal, like an Ibanez Tube Screamer, on the front end of the 2101. I much preferred the punchier (and more versatile) tone of the 12AX7's. In fact, I obtained a set of old Sylvania 12AX7's from a friend of mine and installed them. They have a very smooth high end and a tight focused bottom and are definite keepers! Hope this helps."

Pete Lyall ([email protected]) 9/17/96
"I ended up with the original lower gain Chinese Penta in the V1 socket, and a Sovtek 12ax7wxt in the V2 socket (2 distorted tube voices). Putting a 12ax7wxt in the V1 spot made the first stage a bit too gainy and rough, especially for the clean tones."
Patrick M. O'Hara ([email protected]) 9/16/96
"I just replaced the two in mine with GT's and I honestly can't hear a difference. I did the same with my power-amp this spring and was impressed, so I don't think it's just my ears."
Larry ([email protected])May 1996:
Q - "A question: has anyone tried 12AX7Rs? I read that they're supposed to have more high end and better lows, but I've never actually heard them." - Brian Hansen

A - "I've tried both Groove Tubes 12AX7Rs and Mesa 12AX7As. Very different sounding tubes. The GT's seemed to be more hi-fi, with a much clearer tone, especially on the clean tube setting. They also sounded more "saggy" and less compressed when driven hard. However, on the saturated distortion setting, they seemed to sound more gritchy and less smooth in the high end than the Mesas. I think the GTs would be good candidates for a vintage tube amp that relies on power tube distortion for its tone. I personally preferred the punchier and smoother distortion of the Mesas, even though they didn't sound as crystalline as the GTs on the clean tube setting. Guess ya can't have everything." -[Note: you could use the Groove Tube in V1 for clean tones and a Mesa tube in V2 for the 2nd stage of distorted gain - some people have tried this with positive results.]

Brian Hansen ([email protected]) May 19 1996
"I don't know how much difference the Mesa's vs. GT's would be in the Valve FX, but I put a Mesa SPAX7 in my Valve FX, and I've been really pleased with the response so far. The clean tube has a very nice warm and smooth sound to it, while the distorted and saturated tube settings has much more warmth and dynamic control. I've found that I've lost the characteristics of the Valve FX when it had its original tube in it, but the change over has been well worth it. There is a slight loss of gain, but the additional tonal characteristics well make up for it. I just wish the SPAX7's didn't cost so much. I can get standard Mesa 12AX7's for about 8 a piece, but the SPAX7's run me about 16 a piece."
Pete Lyall ([email protected]) May 21 1996:
"The V1 tube (labelled socket) is used for CLEAN TUBE. Both tubes V1 and V2 are used for the two distorted tube voices. I ended up putting the original PENTA back in V1 (better sparkle) and I stuck a SOVTEK 12AX7WXT in the V2 slot. I can now dial up anything from edgy to total saturation, as well as having a pretty nice clean tone as well. Best of both worlds."
Steve Schow March 13 1996:
"I personally use Sovtek's in mine(those are the Russian ones). There are 3 12AX7 models that I know about.....
12AX7 XT
12AX7 WB
12AX7 _A
From what I understand, no one uses the 3rd one any more. Its either the Xt or the WB. I can't even remember which one I have. I do want to try some others for comparison. But the XT is supposed to be a little higher gain...the WB is supposed to be quieter....pick your poison.

All I can tell you is that the Sovtek Tube I put in is a LOT more consistent, smooth, controlled, predictable, tighter...etc... I think it sounds better. True, for that totally ballsy, out of control marshall sounds, I'm not sure which sounds better. I need to do some A/B-ing.... But it has plenty of gain. With my Strat(single coil pickup) I have gain set to around 8 on each tube....or even less, for a killer crunch rythmn tone. For leads I can go all the way up to 11....and that is usually too much for anything I have ever wanted to do. So I think there is plenth of gain there. But my sound is much more "defined" now. Its tighter and more defined....that's probably the best explanation."

NOTE: Actually, I believe that the 12AX7_A tubes are generally considered standard in musical applications due to their increased immunity to microphonics. Therefore, I would find it hard to believe that they are no longer used. Perhaps, though, these two other types have similar microphonics rejection qualities, and Sovtek decided to market them more.

Mike Caswell ([email protected]) March 14 1996:
"Well, I installed my new Boogie tubes yesterday, and quite frankly I cannot tell the difference. I swapped back and forth between the new set and the old set several times, and the both sounded pretty much the same.

Chances are that there is a difference, but my ears are just not sensitive enough to detect it. Then again, these tubes are "A" types, which may not be all that different from the stock tubes (other than just being "higher quality")... should I try the other variations? WXTs?"

Steve Schow May 19 1995:
Well I bought the 12AX7WXT Sovteks. At this point I am totally confused as to which tubes are which from which manufacturers. The WXt definitely sounds better than the chinese stock tubes in terms of smoothness or crispness....tightness. But I wouldn't really say that its ballsier.....which is what I thought it would be. AT the time I didn't really realize that there are more than one kind of Sovteck, when I bought them. I just thought, call up the place and order some Sovteks....which is what I did and I got the WXT's. If there are others that are ballsier, then I would really like to check those out.
Sovtek Web Page

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Written by Curtis LeMay Pastor,
[email protected] or [email protected]
Last revised as of Jan 22, 1998.