Roadster (Road King) on steroids

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bandit2013

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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.
 
Just a quick note regarding the Multi-Watt Dual Rectifier; I was tube rolling this amp as well but wound up with the stock tubes in the preamp. The Mullard re-issue or Gold Lion B759 reissue would sill work in the phase inverter position. However it will create a low frequency hum in V2 since that tube position heater circuit uses AC. Roadster runs DC to the heaters of V1 and V2. The JAN/GE 12AX7WA will work in the cathode follower positions V3, V4 without issue. I did try loading the preamp with all of the JAN/GE 12AX7WA and the JAN/GE 5751 in V1 and found the amp increased in brightness levels. I feel the MWDR is bright enough with the stock tubes. I do have other NOS tubes on the way so will see how they work out. RFT ECC83/CV4004/CV492 and two medium-long plate Ei CV492 (ECC83). I may even try them in the Roadster to see what happens.
 
For those interested I did make a video of the Roadster with the new complement of preamp tubes. Note that I was using an oversized 412 cab loaded with EVM12L Black Labels with the Roadster. Also near the end of the video I pulled in the Multi-Watt Dual Rectifier that still has all of its original preamp tubes in it and this amp was using the Standard Mesa 412 cab. Yes, the standard is the same size as the old oversized cabinet. The older cabinet that I have came from 1999/2000 and it would flub out so the fix was change in speakers to EV. The newer cabinet that I bought in 2014 was specifically for the Royal Atlantic which explains the gray and black jute grill. Looking to get another 412 cab so I can return the RA100 head back to its throne. Here is a link to the video. Since I am not a sound engineer the balance between the Roadster and Multi-watt is a bit off also had to reduce the output volumes on both amp due to clipping the mic preamp. :roll:

https://www.youtube.com/watch?v=z_hRodX-9Mw&t=42s
 
Old thread I know but I'm curious and have a question. Would this tube roll work in a Rev G Dual Recto or Rev F Triple Recto since they or non multiwatt dual and triple rectos?
 
Old thread I know but I'm curious and have a question. Would this tube roll work in a Rev G Dual Recto or Rev F Triple Recto since they or non multiwatt dual and triple rectos?
Sorry to take so long to respond. I have been absent from the forums for some time. That 4 years of absence went quick. Just been so busy with work these past few years, due to change in leadership and reorganization, now it happened again at the beginning of this year.

Please forgive my ignorance on the Rev G and Rev F. I may as well include the pre-500 (I understand the meaning but not sure what is different).

There could be some risk to exploring different preamp tubes. Now that things cost more these days. Limited resources and the like. In some cases you may find the JAN GE 12AX7WA may be too hi-fi sounding. If you need more brightness to your tone, it may help in the tone stack driver V3. If you want the amp to be more dynamic and add some darkness, the RFT 12AX7A will do it in V2. Never tried that in the cold clipper circuit though. It is sort of tempting.

The JAN GE 12AX7WA would probably work out in the V3 and V4 positions. V3 has that DC coupled cathode follower to drive the tone stack, and V4 associated with a cathode follower but the grid is not DC coupled. This seems to be the trend from the solo heads to others. Not sure what makes the Rev G or Rev F different. The Roadster is laid out differently but does have some common triode circuits to the solo (3CH).

For V1, in the non-MW Rectifiers, I would not use a 5751 tube as it may not be ideal in the other Rectifier models. I does not mean you cannot experiment with this. The stock tube should be ok. However, the V2 position lends itself for exploration potential. The same would apply to the phase inverter V5. Mullard long plate reissue may be ok for the phase inverter. It has a thicker tone than the Sovtek LPS tube even though they look identical. It seems the phase inverter circuit is about the same between the different versions. The dual rec 2CH has only one bypass cap on V2A, 1uF with a 47k resistor that can be bypassed with a relay. That just brings in a bit more low end. V2B is that circuit with the 39k cathode resistor. The Solo version (3CH) retains the 1uF cap with a non-bypassed resistor (100 ohms) for more depth in tone, there is an additional 15uF cap that gets pulled in with a relay for more low end. That circuit is more related to the Roadster. Since I do not have those amps and am not familiar with there characteristics, hard to tell what the side effects will be. If I had the schematics for the MWDR just to see what is similar to the older versions, I would explore V1 and V2 with a variety of different preamp tubes.

Totally unrelated but similar (just has different tube locations for the Cathode followers)
Sort of makes me wonder how the Badlander is related to the Rectifier preamp section. It is obvious where the cathode follower circuits are with that amp (V2 and V4) so that leaves V1 and V3 as exploratory tube positions as well as the phase inverter. I have not tried tube rolling the BL yet.
 
The Tung sol will do fine in V1. Not even sure why I was tube rolling this amp in the first place. Perhaps to get it on par with the MWDR or just to have a change in characteristics.
 

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