If people are interested, here's the post that started this thread, which the OP deleted a few years later, c/o the Wayback Machine.
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This is about my MarkV - I see people struggeling to get a heavy saturated musical tone from it the same I did - this will help!
I bought my MarkV back in 2010 on a holiday trip to cali and since then, I had to learn how to set it up - before, I played a dual recto 3CH which could never meet the tone I was expecting and I hated to use any pedals. The MarkV on the other hand came much clother to the tone I heared in my head, but there where always some fizzy or cold treble frequencies that I couldn't dial out.
The amps FX loop section is bright and adds brightness to everything you play. In the meantime I understand the reason and know how to get rid of that. This is what I want to share with you.
The ice pick or fizz issue is always there, mainly in CH3. The simple cause, that makes it nearly impossible to dial out is that it is generated late in the signal chain, at the end of the preamp. To disable the FX loop makes it better, but I didn't want to lose the solo function and the FX loop. The only thing you can do with standard tube configuration is to keep the chanel master low (I wrote about that secret tone control in another threat), but there is a far better solution:
There is one preamp tube that is golden and perfect to me - back in the days, it cured all troubles I had with my laney, peavey or orange and it cures my MarkV trouble as well. It is the Jan Philips 12AT7. And on the MarkV it belongs on V6, the last stage just before the PI. One triode of V6 contains the last gain stage of ch3, the other triode is the fx loop/solo stage. Compared to 12AX7 it sounds big, fat and nothing but sweet in the higher frequencies and never harsh or cold. It has only 60 percent of gain - and that is maybe the main reason why it will not generate any further treble distortion or ice pic - it just fatens up the tone and lets you dial in more usable sustaining gain that you could think of. It simply cuts out all the harshness.
The funny thing is that you can still dial in more high frequencies than you would ever need. Just use the EQ. The missing level can easily be compensated by turning up the send level (mine went from 10:30 to 02:00).
With the 12AT7 in V6, the highs are not longer dominant. The consequence is that you can dial in more gain, which adds so much sustain and brutality to the sound. The MarkIV mode as well as the MarkII mode can deliver heavier tones then before.
Here is a video I shot just half an hour before my bandmates arrived to rehearsal - random noodeling, so please be patient with my playing
Unfortunately, I don't have any high quality recording equiptment at my rehearsal space, but when you listen to the video I think you get the idea of the tone.
https://pl.vc/1ksxbg setting
https://www.youtube.com/watch?v=PbTDvYfRMwI video
Mesa MarkV (2010) - Mark IV Mode // 90 Watt // Full Power
Preamp: V1-V5: EH12AX7 // V6: Jan Philips 12AT7 // V7: Sovtek 12AX7LPS
Poweramp: TAD 6L6GC-STR // JJ GZ34 (for a heavy 10 Watt Mode)
Mesa 412 std slant & Mesa 112 Thile EV Speaker [Clone]
Ibanez RG Prestige 3620 (Mahagoni with DiMarzio D-Sonic) thru Sommer Spirit XXL Cables
Tell me what you think - greetings from bavaria!