V:90 V4 - 12ax7 low gain options?

[rarebitusa]

Yes there's a bunch of threads on this topic

Tube Rolling is one

@mace had this one

V & VII high gain

But is it ok to have another?

So I've been running a JAN 12AT7 7WC in V4 ever since the V:90 showed up years ago. Initially Ch 3 felt harsh so out with the Mesa STR SPAx7-A that was in there, this made a big difference to my ears. However this was when the learning curve was steep with the amp. It was the core amp in the studio, but have now transitioned it to my live rig. Much has changed (signal chain, axes, cabs) as it's getting alot more time and focus these days.

It still has the 12AT7 in V4 but now starting to feel like Ch 3 could use a bit more gain and maybe it's time to evaluate a 12AX7 again. Don't want a return to the harshness, so perhaps there is "lower gain" 12AX7 to try? Will admit I'm not a avid tube sniffer and paying premiums for some hyped tubes just hasn't worked out for me in the past. I think @bandit2013 mentioned the JAN 5157 wondering if there are other suggestions?

I've got some JAN – GE USA (83), a few ECC83s and some newer Mesa branded 12ax7s laying around. But it I do go tube shopping wondering what's a good one to look at.

 

[Nandrewjackson]

I had to search for this image, I think it's from tube retailer tubestore.com.

 

[Nandrewjackson]

Each of those types have different characteristics other than gain, like current, transconductance? , etc, but they are generally accepted to be interchangeable without catastrophic results.

 

[rarebitusa]

Each of those types have different characteristics other than gain, like current, transconductance? , etc, but they are generally accepted to be interchangeable without catastrophic results.

ok cool I see where the 5751 is placed and why Bandit mentioned it. I'm wondering if there is anything inbetween?

 

[bandit2013]

You know it is not mandatory to use the 12AT7 in V4. That circuit may be high gain but has no influence on the amount of perceived gain you are hearing. V4B is part of the asymmetrical distortion circuit and is more of a boosting stage, V5A is where the distortion takes place as it is forced into overdriven condition due to the gain setting control. So, if you use a weaker tube in V5 and V4 (not something as aggressive as the 12AT7) you will reduce the effect of gain or distortion. Something like the 7025 or MG in both, you can even run the Svetlana tube in those positions as well. This is where you begin to appreciate the level of tuning you can do with the Mark V90.

I found that this characteristic seems to be a trait to the V90 more so than the other amps that may be similar. What works in the V90 will not work in a Mark VII or JP2C. (The IIC+, III and IV are all similar in design with change in some parts here and there). Perhaps it is due to the two additional gain stages, V3A and V6A that allow for tailoring the lead drive circuit. Note that what you stick into V1 and V3 also have an effect on what the outcome will be. Try to view it as a whole and not just in parts as this is a full cascade when using CH3. There may be parts of a tube used with just CH1 or CH2. V2 is the only isolated tube used in CH2 only. The rest are shared in all circuits, some triodes may be used in CH1 and CH2 in the case of V3B, V3A is used on all channels.


There may be a few that sort of fall in between. Not all 7025 will have the same characteristics of the 12AX7 but many will. However, there are a few worth mentioning.

• EH 7025 You can read about its description here:

https://www.thetubestore.com/electro-harmonix-7025-eh

• There is a Mid-Gain JJ tube, the ECC83-MG supposed to fall in between the 12AX7 and 5751.

https://www.thetubestore.com/jj-ecc83-mg-12ax7

• This is a 12AX7 but fall a bit short on the gain characteristics. JJ ECC803s. It is a long plate version and not as much gain as the ECC83s. It is claimed to have high gain, It did not seem to be so when I tried them.

There are other varieties of 12AX7 that work in the Mark V90 to cut some of its harshness.
the Mullard CV4004 used in V4, V5 and V6 was the combination I was running before the saturation mod thread. The Mullard 12AX7 reissue in the same positions will also help too. Fixed the ice pick mostly.

Since I was having other issues with harshness in the other channels like Edge and Tweed modes. Not to mention a low frequency hum I was getting on the clean channel which got annoying. Using a

• Svetlana 12AX7 in V1 and V3 with a tung Sol 12AX7 in V2 fixed the sour itch on the tweed and edge along with eliminating the hum I had on the clean and fat modes.

Any change you make to V1 and V3 will affect all 3 channels.

When I was exploring the JAN 5751, it was mostly for use in V1. I did try it in V4 that was some help. Not as dramatic as the 12AT7 though.

The Svetlana, Tung Sol and Mullards I mentioned are all current production tubes. The 5751 is a NOS tube, a bit pricey but has better qualities than the current production 5751 tubes out there which are just the 12AX7 that is not suitable to be classified as such. I read that somewhere but may not have merit.

• JJ has a 5751 tube.

https://www.thetubestore.com/jj-5751-tube


I had found this a long time ago, but I see it has been updated. This is based a simple amp circuit that relates to the changes in frequency what the low, mid and high end gain is. I would use it as a rough gauge as I doubt the circuit was specifically forcing the signal into distortion. That is the role of V5A. However, the chart may be of some value.

https://www.guitarsite.com/12ax7-comparison-of-current-made-tubes/

 

[MarkV User]

I won’t do it today but I’ll publish what I’ve done to my amp. Unfortunately I don’t have a tester for preamp tube amplification factor. But I can at least say which ones I switched to 12AT7’s. I don’t even remember whether I left the 12AU7 in the phase inverter. That made a potent difference and I think it ended up being too much. At first it was most of positions that I reduced, and then I got great tone but no access to higher gains.

Then I restored one of the early positions like V1 to a 12AX7. I kept playing around and somehow ended up getting channel 1 to be hotter and channel 3 only to be less hot. I was referring to the schematics to plan each next move. I think I spent one or two full days on it, and I had a big box full of preamp tubes to start with. I find this super annoying! To me it means the folks at Mesa didn’t take the time to choose the correct resistor values to make the amp sound good. I fully believe that with a little more of this playing around I can also have a hot channel 3 that sounds “higher gain” even though what is really happening is that the clipping is being distributed over different stages. And when Mesa sends a Mark V amp out to some YouTube personality for testing they have clearly worked he amp super hard to make it sound amazing.

Well, I don’t have any 5751 tubes but I will get some. One thing I recommend is to do the experimentation with tubes you can buy new and that are not too expensive. I haven’t done that strictly because I bought a big box of mixed tubes cheap off Craigslist. For all the trouble we go to we should build gain testers or curve tracers to be sure of the characteristics of these various tubes.

 

[rarebitusa]

However, the chart may be of some value.

https://www.guitarsite.com/12ax7-comparison-of-current-made-tubes/

oh that is a good one... thanks