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This is not a review in the traditional sense, this is more about looking for the ultimate tone out of a great device. I did tubetonening the Groove Tubes Trio preamp in the search of the ultimate tone.
My testbed is one of the 2005 25th Anniversary Silver Edition Groove Tubes Trio which came stock with five GT 12ax7, which are in fact special tested and selected JJ ECC 83 S (ECC 83 is the European name of the 12ax7). The JJ is a Slowakian tube, which is known for its darker top end, and is called a copy of the famous TFK (Telefunken) ECC803 S. This is supposed to be a great choice, but that doesnt work out the potential of the three different voiced circuits.
Tubetonening is now an issue for you if you want to work out the characteristics of the channels more strongly or if you have the gain and/or volume settings at the extreme low or high settings.
If you open the top of the Trio by untightening the screws, you see the five preamp tubes. The first two from left to right called v1 and v2 are working in the Scream channel. The Gain knob works between the first and the second stage of v1 (important to know that one 12ax7 has two independent gain stages in one glass container). With bringing in a lower amplification tube in v1, you have to go up with gain knob and get a more sensible dialing in for mild distortion sounds, but give up the extreme settings. A lower amplification variant of double triodes are the 5751 (70% of a 12ax7), 12at7 (60%), 12au7 (44%) and the 12ay7 (20%). In most applications you can work with the first two, since the 12ay7 draws a lot of current and can cause trouble by overstressing low-wattage plate resistors (they can develop crackling noises over the years).
I found it pleasing to set a UOS Mullard 12at7 (M8162 or CV4024 are identical) in v1 and a 5751 (RCA 5751 blackplates) in v2, this brings the over-the-top screaming (think of a JCM 800 or 900) into a more vintage like distortion. The 5751 is a sweeter sounding tube, while the most 12at7 are brighter due to their lower impedance. I have a lot of 12at7 (and also the identical 6201) at hand but only the Mullard brings a full tone that I like for guitar. Another great combination is the legendary OS (old stock) Mullard ECC 83 in v1 together with a RCA 5963 (special blackplate version of the 12au7) in v2. For over the top i tried the OS Mullard in V1 with a gainy Chinese 12ax7.
Next is v3: The first half is the first stage of the Clean channel is covered by v3, while the second stage is on the first half of v5! With v3 you can influence the character of the Clean channel widely. The channel cannot be overdriven easily since the amplification rate was set very low to duplicate the Tweed area clean sound with a 12ax7. Lot of folks like the more raw SVR/Texas sound, which is achieved with hotrodding the Blackface Fender Super Reverb. If you want this, you need a very strong 12ax7, this can be special ordered from some tube dealers. Then go with 10 on the gain and as much as you can on the Volume.
On the other hand you can dial in a more funky, mid scooped clean sound which is easily done with a lower gained TFK or a Sylvania / american made JAN Phillips or Mullard 12at7. Even a Dutch made Phillips (also labelled as Amperex and Valvo), a Tungsram or a EI is a good choice here the stock GT 12ax7 is too sweet for funky style.
The second stage of v3 it the first stage of the Mean channel. So a hot 12ax7 in v3 (for Texas sound) makes also the Mean channel more crunch up. I had the best results with Mullard 12at7 in v3, which makes the Clean Ch. bright n cutting, but also the Mean Channel a bit softer with a more grainy Tweed area distortion.
The v4 is now the second and third stage of the Mean Ch., which is a Cathode Follower Circuit. This is a special circuit found in Tweed Fenders and the first Marshalls. In theory this is a linedriver (first gain stage) and buffer circuit (second gain stage). This is doing more of compression and buffering than of influencing the amount of distortion or gain. Due to the Cathode Follower Circuit the best tube is a harder to get 12DW7 like the newer JJ ECC 832. It changes more the impedance than the gain. Nevertheless be sure using a tube brand, which reacts smoothly on heavy compression in this slot. The vintage german tubemakers in their heydays tried to push the line of distortion in a preamp tube further away. So the TFK and the Siemens AX7 dont take gain well. They become gritty and nasty at best, if they got a real load of input into the second gain stage with a high impedance not a good choice in this slot. The Mullard or a RCA 12ax7 on the other hand is well known for its capability to take lots of gain in the input, therefore they would be a great choice in here. A 5751 is bit too brown in my book, a 12at7 is a better bet, but the 12au7 made it sound too wimpy IMHO. My best bet so far was the JJ 832 or a spendy UOS Telefunken/Siemens ECC 801. In conclusion, the Mean channel has its very own specific Tweed bassman circuit, on which you have to work for best results.
The V5 is the second stage of the Clean channel and the overall amplification of the preamp which calls for a clear and bright tube. The TFK, together with Sylvania and the Phillips or a Valvo are a good choice there. If you look for the SVR/Texas tone for the Clean I would look for a RCA or GE 12ax7 or even the stock GT here.
All in all, there were my first impressions on the stock 2005 Trio that it has a not overly appealing, very dry Clean and two similar sounding distortion channels. After some tweaks i got a funky Clean, a Mean channel which is a syrupy kind of crunching up with hard playing (think of ole Keef with Micawber) and a vintage sounding Marshall distortion on Scream with a boost.
One word to the Scream Channel: If you choose the 1+3 option, the Gain knob of the Clean reacts as a smoothing down the overdrive of Scream. That means, if you have the Gain knob the Clean nearly full open, both options sound quite identical. If you have a lower setting (see my funky Clean setting), you have less distortion on the Scream. My fav is Gain on about 5-7 for a vintage Marshall sound with the 1+3 option.
Another thought about NOS (New old stock) tubes and UOS (used old stock) tubes: I got both, I never had a problem with them. My UOS are mostly off Ebay, even from American sources. I always looked on their number of deals and the comments about their deals. It was never let down and I got great tubes for a reasonable price. Especially those RCA 5963 or 5751 Blackplates or the Mullard 12at7 are great and durable stuff - will surely last some thousand hours in this unit.
My testbed is one of the 2005 25th Anniversary Silver Edition Groove Tubes Trio which came stock with five GT 12ax7, which are in fact special tested and selected JJ ECC 83 S (ECC 83 is the European name of the 12ax7). The JJ is a Slowakian tube, which is known for its darker top end, and is called a copy of the famous TFK (Telefunken) ECC803 S. This is supposed to be a great choice, but that doesnt work out the potential of the three different voiced circuits.
Tubetonening is now an issue for you if you want to work out the characteristics of the channels more strongly or if you have the gain and/or volume settings at the extreme low or high settings.
If you open the top of the Trio by untightening the screws, you see the five preamp tubes. The first two from left to right called v1 and v2 are working in the Scream channel. The Gain knob works between the first and the second stage of v1 (important to know that one 12ax7 has two independent gain stages in one glass container). With bringing in a lower amplification tube in v1, you have to go up with gain knob and get a more sensible dialing in for mild distortion sounds, but give up the extreme settings. A lower amplification variant of double triodes are the 5751 (70% of a 12ax7), 12at7 (60%), 12au7 (44%) and the 12ay7 (20%). In most applications you can work with the first two, since the 12ay7 draws a lot of current and can cause trouble by overstressing low-wattage plate resistors (they can develop crackling noises over the years).
I found it pleasing to set a UOS Mullard 12at7 (M8162 or CV4024 are identical) in v1 and a 5751 (RCA 5751 blackplates) in v2, this brings the over-the-top screaming (think of a JCM 800 or 900) into a more vintage like distortion. The 5751 is a sweeter sounding tube, while the most 12at7 are brighter due to their lower impedance. I have a lot of 12at7 (and also the identical 6201) at hand but only the Mullard brings a full tone that I like for guitar. Another great combination is the legendary OS (old stock) Mullard ECC 83 in v1 together with a RCA 5963 (special blackplate version of the 12au7) in v2. For over the top i tried the OS Mullard in V1 with a gainy Chinese 12ax7.
Next is v3: The first half is the first stage of the Clean channel is covered by v3, while the second stage is on the first half of v5! With v3 you can influence the character of the Clean channel widely. The channel cannot be overdriven easily since the amplification rate was set very low to duplicate the Tweed area clean sound with a 12ax7. Lot of folks like the more raw SVR/Texas sound, which is achieved with hotrodding the Blackface Fender Super Reverb. If you want this, you need a very strong 12ax7, this can be special ordered from some tube dealers. Then go with 10 on the gain and as much as you can on the Volume.
On the other hand you can dial in a more funky, mid scooped clean sound which is easily done with a lower gained TFK or a Sylvania / american made JAN Phillips or Mullard 12at7. Even a Dutch made Phillips (also labelled as Amperex and Valvo), a Tungsram or a EI is a good choice here the stock GT 12ax7 is too sweet for funky style.
The second stage of v3 it the first stage of the Mean channel. So a hot 12ax7 in v3 (for Texas sound) makes also the Mean channel more crunch up. I had the best results with Mullard 12at7 in v3, which makes the Clean Ch. bright n cutting, but also the Mean Channel a bit softer with a more grainy Tweed area distortion.
The v4 is now the second and third stage of the Mean Ch., which is a Cathode Follower Circuit. This is a special circuit found in Tweed Fenders and the first Marshalls. In theory this is a linedriver (first gain stage) and buffer circuit (second gain stage). This is doing more of compression and buffering than of influencing the amount of distortion or gain. Due to the Cathode Follower Circuit the best tube is a harder to get 12DW7 like the newer JJ ECC 832. It changes more the impedance than the gain. Nevertheless be sure using a tube brand, which reacts smoothly on heavy compression in this slot. The vintage german tubemakers in their heydays tried to push the line of distortion in a preamp tube further away. So the TFK and the Siemens AX7 dont take gain well. They become gritty and nasty at best, if they got a real load of input into the second gain stage with a high impedance not a good choice in this slot. The Mullard or a RCA 12ax7 on the other hand is well known for its capability to take lots of gain in the input, therefore they would be a great choice in here. A 5751 is bit too brown in my book, a 12at7 is a better bet, but the 12au7 made it sound too wimpy IMHO. My best bet so far was the JJ 832 or a spendy UOS Telefunken/Siemens ECC 801. In conclusion, the Mean channel has its very own specific Tweed bassman circuit, on which you have to work for best results.
The V5 is the second stage of the Clean channel and the overall amplification of the preamp which calls for a clear and bright tube. The TFK, together with Sylvania and the Phillips or a Valvo are a good choice there. If you look for the SVR/Texas tone for the Clean I would look for a RCA or GE 12ax7 or even the stock GT here.
All in all, there were my first impressions on the stock 2005 Trio that it has a not overly appealing, very dry Clean and two similar sounding distortion channels. After some tweaks i got a funky Clean, a Mean channel which is a syrupy kind of crunching up with hard playing (think of ole Keef with Micawber) and a vintage sounding Marshall distortion on Scream with a boost.
One word to the Scream Channel: If you choose the 1+3 option, the Gain knob of the Clean reacts as a smoothing down the overdrive of Scream. That means, if you have the Gain knob the Clean nearly full open, both options sound quite identical. If you have a lower setting (see my funky Clean setting), you have less distortion on the Scream. My fav is Gain on about 5-7 for a vintage Marshall sound with the 1+3 option.
Another thought about NOS (New old stock) tubes and UOS (used old stock) tubes: I got both, I never had a problem with them. My UOS are mostly off Ebay, even from American sources. I always looked on their number of deals and the comments about their deals. It was never let down and I got great tubes for a reasonable price. Especially those RCA 5963 or 5751 Blackplates or the Mullard 12at7 are great and durable stuff - will surely last some thousand hours in this unit.