My interest have picked up considerably with the Roadster ever since I got the Mulit-Watt Dual Rectifier. This happens with me when I get amps of the same family or series as I like to find out where the similarities are and where they differ. Mind you this is not to evaluate which amp is better than the other but how I can make use of both amps in a rig as well as what I have done to improve the character of the Roadster to better serve my needs. Also I was never fond of running any OD or boost pedals on the front end as that tends to kill the character of the amp and sound fizzy or buzzy. The tube cocktail I wound up with does not require external gear to tighten up the amp. Here is what I wound up with in the Roadster preamp section:
V1: JAN/GE 5751, V2+V6: Mullard re-issue 12AX7, V3+V5: JAN/GE 12AX7WA and V4: stock. I still have the stock Mesa 5U4GB and Mesa 6L6GC STR440 (yellows). I did a post a while back about using a JAN/Phillips 12AT7 or RFT 12AT7 in V6. That was ok but this last tube roll I did took the Roadster to another level, OMG level to be exact.
You do not need to read any further, but if you want details why I chose this combination you can read on.....
Contiuation from above, it gets long from here... (you can skip to the next paragraph if you want just the meat) If you are going to compare two amps, it is always best to go to the stock tubes (does not have to be the original tubes the amp came with but stock tubes does take things back to the root characteristic of the amp in question). Sometimes there is that endless search for alternative preamp tubes to find an answer to a question regarding what preamp tubes can be used in the cathode follower circuits. We all know (or should know) that current production tubes out of Russia, namely the Reflektor tube factory in Saratov that is brokered by New Sensor under many trade names (Tung Sol, Gold Lion, Mullard, Svetlana, Sovtek, Electro Harmonix, and probably others.) Nothing wrong with those tubes however the issue with then in the design of the cathode and heater element such that they will not survive for long in a cathode follower circuit. So what do we get stuck with? Stock Mesa (JJECC83) will do the job quite well in the cathode follower positions as will the Chinese variants of the 12AX7 tubes, Sino has a few variants, Ruby, Preferred Series, TubeAmpDr and I believe there is version of one of these sold as a Gold Lion Standard ECC83, look close and you will see made in China. It is the ECC83/B759 premium tube that is made in the Saratov-Reflektor factory that you should not use in a cathode follower position.
The main point (beef to the discussion starts here): Wtih the stock tubes installed in the Roadster it may not behave like the beast you expect it too. Also with an oversized 412 cabinet the tone of the amp may get into mud or swamped in too much low end that there is a lack of top end character. This is mostly in effect with CH4 and CH2 does sit a bit darker than CH1. This was done by design to give you 4 distinct channels. Some who have the Roadster may spend more time on CH3 due to it being brighter but it also has a lower gain than CH4 but not by much. I have been tube rolling this amp for many years to find the best combination that I feel deserves some attention. Some of my tube choices may make you think the amp will have less gain as an end result. Primarily my #1 choice for the V1 position. JAN/GE 5751 had the best overall characteristic than the Tung Sol 12AX7. You may think this tube has less gain as it should, 30% less. So with just a gain factor number 12AX7 should be 100 and the 5751 would be 70. Here is the delima with the Roadster and why the 5751 works better, V1A runs with a 220K plate resistor for CH3/CH4 so it has a high sensitivity, the gain control is a basic adjustable voltage divider to drive V1B. One has to understand these two gain stages also have very large cathod bypass capacitors. Wtih a 12AX7 in V1 you will also get more bottom end than is required and the end result is low end you cannot dial out with the tone controls. The JAN/GE 5751 is a good quality tube that will enhance the amps characteristic by reducing the low end dominance and increasing the high frequency content. It is much brighter than a Tung Sol in general. V2 becomes the critical path tube as it is the 3rd gain stage for both clean and gain channels. The JAN/GE 5751 does reduce the low end and provided a bright tone, we will be using V2 to enhance both clean and high gain. So far what I found works best is a Mullard Re-issue 12AX7 (long plate). For the clean channels, V2A is the last gain stage for the cleans. You will get a full bodied bold tone with the long plate Mullard tube and I also found the volume levels to be a bit louder than they were with the stock tubes. Not only that, the Mullard tube also enhances the midrange and the Tweed and Brit voices sound amazingly better. Brit has that tendency to get harsh but with the change in preamp tubes it sounds much closer to the TC-100/TC-50 and almost identical to the Pushed voice of the Multi-Watt Dual Rectifier. More beef comes next, what we what to read about.. the high gain stuff.
Beef part 2: The voice of the Recto we all have come to love or hate lies in the V2B triode. This circuit is the cold clipper that is responsible for most of that drive characteristic. Since it is basically runnig in diode mode such that the negative switch is clipped and the postive switch is left untouched, since the triode is not a perfect device and has non-linear characterisitcs, you not only get 2nd order harmonic content but the sub harmonics as well. Remember V1? That high gain fist stage does get into a light clip since it is the primary gain stage but that clipped portion of the signal is not affected by the cold clipper crircuit of V2B. The following gain stage V3A is another high gain triode circuit that will now amplify this cold clipped part of the waveform since each gain stage inverts the signal. V3B is the dc coupled cathode follower that likes to eat russian tubes. You can stick with the Mesa 12AX7 if you so desire or use Chinese tubes in V3. I was looking for something different. Ask a few questions and you get answeres. One would think there is not much to gain here but yet there is that high gain circuit in V3A. The importance of the cathode follower immediately following is not just to normalize the signal for the tone stack that follows as it too gets saturated and may be responsible for driven compression. Here is where the JAN/GE 12AX7WA comes in to play. It works quite well in V3. Adds in more high frequency and fills in the bottom end quite nicely. Before I got the JAN/GE12AX7WA I was using the stock Mesa tube in V3 as I preferred that over the Chinese tube characteristics. With this combination of pream tubes I can actually push the bass to 3pm, with a moderate gain setting of 2pm and the amp remains tight, no flub, drone, or what ever is used to describe the issue. Plam muting also sounds amazing. Tight an percussive like it should be with a hint of dry tone and no drone. Next tube in the Roadster is the reverb tube. I still have the stock tube in that position but you can experiment to your hearts content so any tube would work here.
FX loop enhancment: You can also use the JAN/GE 12AX7WA tube in the V5 position. this is optional. I feel it improved the overall tone and may be the reason why CH1 and CH2 have increased in volume relative to the CH3/CH4 level shift. Your effect level will increase a little bit too so you may have to compensate with the send level if this gives you issues. The effect pedals I use now can tolerate the line level inputs so I would not notice any side effects due to the perceptual increase.
The last stage enhancment: Phase inverter. This too is optional and use what ever suits your needs. I prefer matched triode long plate 12AX7 tube for the phase inverter. I used to run with the Sovtek LPS 12AX7 as this added some brightness to the overal character of the amp but also seemed to thin out some of the content. I have not bought any new ones lately so what I have on hand is either worn out. Here is where I like the Mullard re-issue long plate 12AX7 as it does a decent job in keeping good balance across the frequency band of the guitar. Another option is the Gold Lion B759/12AX7 which is similar to the Mullard re-issue in tonal character but adds a bit more top end. These tubes are similar to the Sovtek LPS but are of better quality.
V1: JAN/GE 5751, V2+V6: Mullard re-issue 12AX7, V3+V5: JAN/GE 12AX7WA and V4: stock. I still have the stock Mesa 5U4GB and Mesa 6L6GC STR440 (yellows). I did a post a while back about using a JAN/Phillips 12AT7 or RFT 12AT7 in V6. That was ok but this last tube roll I did took the Roadster to another level, OMG level to be exact.
You do not need to read any further, but if you want details why I chose this combination you can read on.....
Contiuation from above, it gets long from here... (you can skip to the next paragraph if you want just the meat) If you are going to compare two amps, it is always best to go to the stock tubes (does not have to be the original tubes the amp came with but stock tubes does take things back to the root characteristic of the amp in question). Sometimes there is that endless search for alternative preamp tubes to find an answer to a question regarding what preamp tubes can be used in the cathode follower circuits. We all know (or should know) that current production tubes out of Russia, namely the Reflektor tube factory in Saratov that is brokered by New Sensor under many trade names (Tung Sol, Gold Lion, Mullard, Svetlana, Sovtek, Electro Harmonix, and probably others.) Nothing wrong with those tubes however the issue with then in the design of the cathode and heater element such that they will not survive for long in a cathode follower circuit. So what do we get stuck with? Stock Mesa (JJECC83) will do the job quite well in the cathode follower positions as will the Chinese variants of the 12AX7 tubes, Sino has a few variants, Ruby, Preferred Series, TubeAmpDr and I believe there is version of one of these sold as a Gold Lion Standard ECC83, look close and you will see made in China. It is the ECC83/B759 premium tube that is made in the Saratov-Reflektor factory that you should not use in a cathode follower position.
The main point (beef to the discussion starts here): Wtih the stock tubes installed in the Roadster it may not behave like the beast you expect it too. Also with an oversized 412 cabinet the tone of the amp may get into mud or swamped in too much low end that there is a lack of top end character. This is mostly in effect with CH4 and CH2 does sit a bit darker than CH1. This was done by design to give you 4 distinct channels. Some who have the Roadster may spend more time on CH3 due to it being brighter but it also has a lower gain than CH4 but not by much. I have been tube rolling this amp for many years to find the best combination that I feel deserves some attention. Some of my tube choices may make you think the amp will have less gain as an end result. Primarily my #1 choice for the V1 position. JAN/GE 5751 had the best overall characteristic than the Tung Sol 12AX7. You may think this tube has less gain as it should, 30% less. So with just a gain factor number 12AX7 should be 100 and the 5751 would be 70. Here is the delima with the Roadster and why the 5751 works better, V1A runs with a 220K plate resistor for CH3/CH4 so it has a high sensitivity, the gain control is a basic adjustable voltage divider to drive V1B. One has to understand these two gain stages also have very large cathod bypass capacitors. Wtih a 12AX7 in V1 you will also get more bottom end than is required and the end result is low end you cannot dial out with the tone controls. The JAN/GE 5751 is a good quality tube that will enhance the amps characteristic by reducing the low end dominance and increasing the high frequency content. It is much brighter than a Tung Sol in general. V2 becomes the critical path tube as it is the 3rd gain stage for both clean and gain channels. The JAN/GE 5751 does reduce the low end and provided a bright tone, we will be using V2 to enhance both clean and high gain. So far what I found works best is a Mullard Re-issue 12AX7 (long plate). For the clean channels, V2A is the last gain stage for the cleans. You will get a full bodied bold tone with the long plate Mullard tube and I also found the volume levels to be a bit louder than they were with the stock tubes. Not only that, the Mullard tube also enhances the midrange and the Tweed and Brit voices sound amazingly better. Brit has that tendency to get harsh but with the change in preamp tubes it sounds much closer to the TC-100/TC-50 and almost identical to the Pushed voice of the Multi-Watt Dual Rectifier. More beef comes next, what we what to read about.. the high gain stuff.
Beef part 2: The voice of the Recto we all have come to love or hate lies in the V2B triode. This circuit is the cold clipper that is responsible for most of that drive characteristic. Since it is basically runnig in diode mode such that the negative switch is clipped and the postive switch is left untouched, since the triode is not a perfect device and has non-linear characterisitcs, you not only get 2nd order harmonic content but the sub harmonics as well. Remember V1? That high gain fist stage does get into a light clip since it is the primary gain stage but that clipped portion of the signal is not affected by the cold clipper crircuit of V2B. The following gain stage V3A is another high gain triode circuit that will now amplify this cold clipped part of the waveform since each gain stage inverts the signal. V3B is the dc coupled cathode follower that likes to eat russian tubes. You can stick with the Mesa 12AX7 if you so desire or use Chinese tubes in V3. I was looking for something different. Ask a few questions and you get answeres. One would think there is not much to gain here but yet there is that high gain circuit in V3A. The importance of the cathode follower immediately following is not just to normalize the signal for the tone stack that follows as it too gets saturated and may be responsible for driven compression. Here is where the JAN/GE 12AX7WA comes in to play. It works quite well in V3. Adds in more high frequency and fills in the bottom end quite nicely. Before I got the JAN/GE12AX7WA I was using the stock Mesa tube in V3 as I preferred that over the Chinese tube characteristics. With this combination of pream tubes I can actually push the bass to 3pm, with a moderate gain setting of 2pm and the amp remains tight, no flub, drone, or what ever is used to describe the issue. Plam muting also sounds amazing. Tight an percussive like it should be with a hint of dry tone and no drone. Next tube in the Roadster is the reverb tube. I still have the stock tube in that position but you can experiment to your hearts content so any tube would work here.
FX loop enhancment: You can also use the JAN/GE 12AX7WA tube in the V5 position. this is optional. I feel it improved the overall tone and may be the reason why CH1 and CH2 have increased in volume relative to the CH3/CH4 level shift. Your effect level will increase a little bit too so you may have to compensate with the send level if this gives you issues. The effect pedals I use now can tolerate the line level inputs so I would not notice any side effects due to the perceptual increase.
The last stage enhancment: Phase inverter. This too is optional and use what ever suits your needs. I prefer matched triode long plate 12AX7 tube for the phase inverter. I used to run with the Sovtek LPS 12AX7 as this added some brightness to the overal character of the amp but also seemed to thin out some of the content. I have not bought any new ones lately so what I have on hand is either worn out. Here is where I like the Mullard re-issue long plate 12AX7 as it does a decent job in keeping good balance across the frequency band of the guitar. Another option is the Gold Lion B759/12AX7 which is similar to the Mullard re-issue in tonal character but adds a bit more top end. These tubes are similar to the Sovtek LPS but are of better quality.