Mark IV simul tube currents.

[boola]

Hi,

Can someone tell me the voltage/current on the tubes when the MarkIV is in simul mode?

The outer 2 tubes glow blue and I think are being used harder. Isn't is annoying that 2 of the tubes will wear out quicker than the other 2....

 

[Whoopysnorp]

There is a lot higher idle current going through the outer pair of tubes in simulclass, so it makes sense that they would be hit harder.

 

[boola]

It depends on the voltage as well, is the voltage the same on the inner and outer pair?

 

[ANIMATED SUSPENSION]

Mine don't glow blue, they look exactly the same (std M/B tubes) with 6L6's or EL34's.
Besides it's not that one pair wears out quicker it's that one pair lasts longer !!

 

[boola]

It's just it means you need to change the outer pair at different times to the middle pair to keep it sounding it's best or maybe swap them over after a while. I've just got some new tubes - maybe I didn't need to replace the middle ones I'll see how they compare after 6 months.

 

[6L6C]

Hi,

Can someone tell me the voltage/current on the tubes when the MarkIV is in simul mode?

The outer 2 tubes glow blue and I think are being used harder. Isn't is annoying that 2 of the tubes will wear out quicker than the other 2....

I have a chart on a Microsoft Word, just go to link and download file

http://www.box.net/shared/thtamz9jr6

If you are concerned about tube life run the amp in tweed. That will drop the plate voltage a bit.

Even with a matched quad of 6L6's the outer sockets will run a little hotter than the inners or really it is the inners run a little cold.

The EL34's on the other hand run cold as hell.

Long as the tubes you have in there are within Mesa specs tomorrow there should not be a problem. it does not hurt to check though. in my chart you will see my outers are slightly hot this is intentional I'm always tweaking!

 

[trem]

in my chart you will see my outers are slightly hot this is intentional I'm always tweaking!

Hey John, are these numbers after or before the bias mod? Thanks.

 

[boola]

Hi,

Can someone tell me the voltage/current on the tubes when the MarkIV is in simul mode?

The outer 2 tubes glow blue and I think are being used harder. Isn't is annoying that 2 of the tubes will wear out quicker than the other 2....

I have a chart on a Microsoft Word, just go to link and download file

http://www.box.net/shared/thtamz9jr6

If you are concerned about tube life run the amp in tweed. That will drop the plate voltage a bit.

Even with a matched quad of 6L6's the outer sockets will run a little hotter than the inners or really it is the inners run a little cold.

The EL34's on the other hand run cold as hell.

Long as the tubes you have in there are within Mesa specs tomorrow there should not be a problem. it does not hurt to check though. in my chart you will see my outers are slightly hot this is intentional I'm always tweaking!

Awesome, thanks! 2 questions though. Are you using MesaBoogie tubes and why is there current going through the middle pair when it's in class A mode?

I'm not concerned about tube life as such, it's just that I wasn't aware that when I change them I might not have to change all 4 as they don't all wear evenly.

 

[6L6C]

in my chart you will see my outers are slightly hot this is intentional I'm always tweaking!

Hey John, are these numbers after or before the bias mod? Thanks.

Those numbers are before the bias mod I was basically just screwing around with different pairs of tubes. The tubes are all SED =C= and they came from Doug. The 4x6L6 are in a pretty good place, I did have some Mesa’s and they were coming in colder especially the EL34’s those numbers were pitiful! But there again as you can see in the chart the numbers for the =C= are pretty cold also. Ironically though put the math aside everything sounded good. And that’s what’s important and of course and not putting the amp in danger.
Well after the mod:

As for the 6L6’s not any place to really go. Doug’s tubes are pretty dam good. When adjusting the bias it is proportional to all 4 sockets and the outer two sockets do run a little hotter by nature. So basically I’m paying attention to the outer sockets and the inner’s are along for the ride and what they are is what they are.
When adjusting the 2x6L6/EL34 I’m doing the opposite I’m paying attention to the inners since by nature the EL34’s are running really cold in this amp. So I would put the inner 6L6’s in a good place and the 34’s are along for the ride. Funny thing when you do adjust this configuration the EL34 seem to hit a point and they snap to life a bit almost like a push over the cliff with numbers more like 8-10 watts.
Just have to remember when going back to the 4x6L6 to re-bias otherwise those sockets are going to be cooking those outer tubes.

As you already know but for the benefit of anyone else reading this, I only got the bias mod for future NOS tubes.


Sentot
What is up with your IV? Did you get everything done yet?

 

[6L6C]

Awesome, thanks! 2 questions though. Are you using MesaBoogie tubes and why is there current going through the middle pair when it's in class A mode?
I'm not concerned about tube life as such, it's just that I wasn't aware that when I change them I might not have to change all 4 as they don't all wear evenly.

Just keep in mind I’m not a tech!

So for your first question really can’t tell you why there is current going through the inners in class A but they are off. The tubes in the chart are all SED’s I do have some Mesa the only real difference is the Mesa’s come in a bit colder over all.
As for replacement if you just want to do a pair I would go for the outer sockets just because no matter what configuration you use those sockets are always on. And also even with a matched quad of 6L6’s running simul-class all the time the outer sockets run hotter (idling current) by nature on this amp.