Mullard reissue 12AX7 in Mark V

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bandit2013

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If you want to supercharge CH2 and give it some grunt without darkening the overall tone I found the Mullard reissue 12AX7 to be the best performer for V2. I have tried many others including the new Mullard CV4004 only to return to the Mullard reissue 12AX7. Sure it looks like a long plate Sovtek, even resembles the Gold lion B759/12AX7. I have tried both to no avail and hands down the Mullard reissue defeats them all (so far).

It will alter the gain structure and tone. CH2 Crunch will become more sinister, Mark I mode a bit more liquid and amazingly the Edge is not as brittle and thin, it sounds more like the Crunch with a much lower gain setting. Highs are still in abundance and you can add more bass to Mark I mode. You can also enhance the tone and gain structure with a 7025 (Preferred series, Ruby HG, or even the Mullard CV4004 in V3. Keeping the Mesa 12AX7A (JJ tubes) in all other positions works well too. If you use CH2 considerably but feel it may be drowning in the lows too much or just does not have enough bite, the long plate Mullard reissue 12AX7 will definitely fix it.

I have tried running two Mullard reissue tubes with mixed results. (V1 + V2) and (V2 +V3) as well as three (V1, V2, V3). The V2+V3 sounded the best. I prefer to keep the amp tight so V2 and V1 are 7025 type tubes (12AX7) like the Ruby HG or (Preferred series which is the same thing). However the Mullard reissue performed well in a triad arrangement.
 
As of late, I decided to go full tilt with the Mullard reissue 12AX7 in the Mark V.
V1, V3, V4, V5, V6 all Mullard 12AX7 long plate tubes.
V2 (Mesa branded Chinese tube from the 90 (Shuguang 12ax7a with dimpled square getter) really enhances the mids in crunch mode)
V7 is the trusty Sovtek LPS
Rect EH 5U4Gb
Power tubes SED =C= 6L6GC (set from last production).

The Mark V never sounded better. I do like the PS7025 same as ruby, and others like the TAD12AX7, but the Mullards really enhance the gain structure without becoming brittle.
 
After converting the Mark V from a head to a combo I had noticed the Mullard preamp tubes would sometimes ring into oscillation when channel changing. This was primarily caused by voltage shifting when selecting CH3. I really liked the roll off of the high frequencies and the warmth of the reverb circuit but the ringing feedback was becoming annoying. This time I wanted to try something different with the power section. I do like the SED =C= 6L6GC but they can be bright since the Mark V runs a hotter bias than say a Mark IV, RA100 or Roadster. I decided to pull the Mullards and the Sovtek LPS in the PI spot and the SED 6L6 tubes. Wondering what would work best with the Gold Lion KT77, I collected all of the Mesa branded JJ tubes out of the many boxes I had them stored in. Selected the quiet ones (I have many that sound like broken light bulbes when you tap on them, they are still good but may make mechanical noise in the Combo amp). I do not mind the subtle hiss I get with the Mesa tubes, I do have others if needed to roll out the white noise. Wow, I am impressed with the overall tones using the Mesa (JJ) tubes and the KT77. I would use the Mesa STR 440 but I only have one that is good and I have no plans on pulling the quad out of the Roadster. With stock preamp tubes and the KT77, the Mark V combo sounds very close to the Roadster when really driving the CH2 with moderate gain. This is also the first time I was able to enjoy the Tweed mode in CH1. Still do not care much for the Edge voice of CH2 (still remains thin and brittle, all depends on how it is set up). Crunch and Mark I mode are awesome. CH3 is great as always. No more ping or onset of oscillation when channel changing. The long plate preamp tubes are best served in a steady voltage application so that rules out use for V1. It seems like a hit or miss with the Mullard reissue. The Mullard CV4004 seems a bit more compressed than the 12AX7 long plate version. So why the change back to the Mesa JJ tubes? Last month I received a new Roadster and it is perfect with the stock tubes. Just for kicks I did experiment with some preamp tubes and power tubes just to hear the difference. In my opinion it sounds awesome with the stock tubes (just in case the preamp tubes were position sensitive, I marked them so they would go back in their original position after removal.) The CH1 clean and fat sound exceptional, more of that dry acoustic tone that only the Mark IV combo was capable of delivering. The KT77 do not seem to degrade the clean channel tone as the EL34 would tend to provide and early clip of the signal. Best of all, the Bass response in CH2 crunch at 90W is tight and aggressive which is very close to the Roadster CH4 modern set to the legendary DR setting. I wonder how long it will take before I get annoyed with the Mark V and tube roll again. So far it sound great and has lost most of the brittleness common with Class A power amps (I know, the Mark V runs Class A/B at 90W but it is not quite the same as the Class A/B circuit of the Roadster or the RA100 which have a warmer character to it than the Simul Class power section of the Mark Series amplifiers. Actually the Mark V seems to run hotter than the Mark IV which tends to add brittleness to high gain settings with a moderate presence setting. Before the change of tubes, I could not tolerate the tweed mode of CH1 no matter what I did to the channel settings, could not dial out the breaking glass tone (same goes for the Edge voice of CH2 but not much changed with that).
 
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