Mark IIB Simul-Class: Anyone Running 4 x 6L6's or at 4 Ohms?

[DC3 Gridlock]

I am really enjoying learning this amp and am getting good tones.

Curious, I favor the tone of 6L6's better than EL34's and would like to swap the two outside EL34's with Mesa branded 6L6's to run at 15 watts.

I have read threads stating that the 6L6's fry in these slots but I recently contacted Mesa and they stated that I could run 6L6's in these two slots.

Also would I hurt that amp running it into the 4 ohm tap (standard EVM-12L speaker) and what differences in tone and volume could I expect?

Thanks ahead of time.
Grid

 

[DC3 Gridlock]

I am sure their is some great knowledge on the Mark amps out there in Mesa Boogie land.
Anyone...

 

[MrMarkIII]

Sure, 6L6's are fine in the outer sockets. At one time, 6L6 quality was poor, so Mesa recommended against them, but it's cool now.

Running from the 4 ohm tap yields a compressed, thinner, more "distant" tone. My opinion. I've run my MkIII since 1990.

The power tubes wear out faster when there is a speaker mis-match. Either way.

This is what my 1990 Mark III Simul-Class manual states:

"... with an 8 ohm speaker plugged into the 8 ohm jack, the amp clips at about 40 watts (switch down), and 115 watts (switch up).
But with an 8 ohm speaker in the 4 ohm jack, the amp clips at about 60 watts (switch down) and 80 watts (switch up) and the tone is slightly different..."

(The manuals you download at Mesa's website no longer have this passage. The "new" manuals have the bit about using EL-34's in the outer sockets. Which was deleted in even later, even newer versions).

And to further confuse everyone, you CAN run a Simul-Class amp with only the OUTER socket power tubes. The switch must be in the "Class A" position (switch down).
You CANNOT run them with tubes only in the inner sockets. When in full Simul-Class mode (switch up) all four power tubes are in circuit.

I'm going to add this simply because this question gets asked almost every day, so it bears repeating:

"One 8-ohm and two 4-ohm jacks are provided. The Boogie is not very sensitive to speaker mismatches and will not be damaged by
them except that very low ohmage loads will cause the power tubes to wear out faster. A single twelve-inch 8-ohm, speaker should
generally be connected to the 8-ohm output on the amp. When using two 8-ohm speakers, connect them both to the 4-ohm outputs
provided (because the total load is 4 ohms in that case)."

 

[DC3 Gridlock]

Sure, 6L6's are fine in the outer sockets. At one time, 6L6 quality was poor, so Mesa recommended against them, but it's cool now.

Running from the 4 ohm tap yields a compressed, thinner, more "distant" tone. My opinion. I've run my MkIII since 1990.

The power tubes wear out faster when there is a speaker mis-match. Either way.

This is what my 1990 Mark III Simul-Class manual states:

"... with an 8 ohm speaker plugged into the 8 ohm jack, the amp clips at about 40 watts (switch down), and 115 watts (switch up).
But with an 8 ohm speaker in the 4 ohm jack, the amp clips at about 60 watts (switch down) and 80 watts (switch up) and the tone is slightly different..."

(The manuals you download at Mesa's website no longer have this passage. The "new" manuals have the bit about using EL-34's in the outer sockets. Which was deleted in even later, even newer versions).

And to further confuse everyone, you CAN run a Simul-Class amp with only the OUTER socket power tubes. The switch must be in the "Class A" position (switch down).
You CANNOT run them with tubes only in the inner sockets. When in full Simul-Class mode (switch up) all four power tubes are in circuit.

I'm going to add this simply because this question gets asked almost every day, so it bears repeating:

"One 8-ohm and two 4-ohm jacks are provided. The Boogie is not very sensitive to speaker mismatches and will not be damaged by
them except that very low ohmage loads will cause the power tubes to wear out faster. A single twelve-inch 8-ohm, speaker should
generally be connected to the 8-ohm output on the amp. When using two 8-ohm speakers, connect them both to the 4-ohm outputs
provided (because the total load is 4 ohms in that case)."

Thanks MrMark,

Loving this amp and it will be a keeper. With your info, I'm going to order a quad match set of Mesa 6L6's soon.

Thanks again.