6V6's in Mark IV

[hackenfort]

I would use the search feature, but don't have enought posts to do so.

So I'll ask a question that's I'm sure someone will know the answer for me

I have a MKIV - the manual says I can run 6V6's in Tweed mode - A/B, is there a reson I couldn't run them in class A mode?

Thank you

kevin

 

[mrmax]

When running 6V6's in the MK IV you must use Tweed Power & Simulclass...otherwise the plate voltage will be too high and destroy the 6V6's and quite possibly damage the amp. I repeat Tweed Power & Simulclass settings when using 6V6's. Try it ,it sounds great!

 

[Blueracer]

This would be worth a call to mesa. I would recommend talking to Mike B regarding this. The lower voltage represented by tweed mode makes sense. However switching between simulclass and class A does not immediately make sense to me. Basically the two inner tubes are effectively removed from the circuit in class A by isolating their cathods. This would not change the operating conditions on the outer two tubes. There may be some subtley in the impedance seen by the outer tubes in class A which is not immediately evident and is different than in simulclass. Note also that the manual recommends using an 8 ohm speaker into the 4 ohm output. This is a mismatch but it does limit current draw on the tube.

My understanding of newer 6V6 tubes is they are not as resilent as the older 6V6 tubes. A set of NOS might be able to withstand the higher operating conditions than the newer tubes. Fender used this to advantage in their old BF Deluxe Reverbs which had a plate voltage of 415 volts while the tube was spec'd at a maximum plate voltage of something like 350 volts. I believe that the JJ 6V6 tubes are able to withstand higher operating voltage.

Whatever you do you are kind of on your own as the manual is very explicit as to how the 6V6s are to be used.

Hope this helps.

 

[phyrexia]

I think most people have measured that the outer sockets get more juice when in class A than when in simul class.

JOEY B, you there?

 

[Blueracer]

There may be less voltage drop across the output transformer (dc wise) without the current draw of the inner tubes which would raise the voltage of the outer tubes. That may account for the simulclass only thing in the manual. I am kind of thinking out loud here. Any direct experience or measurements would be helpful on this.

 

[hackenfort]

Thanks for the info guys, I'm off on vacation for about 10 days, when I get back home. Looks like a call to Mesa to see what they think

Take care

kevin

 

[Axis39]

I have a set of 6v6's in my Mark IV right now. The manual says to run it in Simulclass and on Tweed. Seems to be working just fine on my amp. No excessive heat and some very nice tone.