Mark 3 simul-class?

[Generic Jeff]

Hello to all.
I have a Mark 3 long chassis head (black dot) with Sovtek 5881's in the output section. Here are a few newbie questions for yas all.
I'm a little confused about the 60/100 switch on the front of the amp. It does have simul-class stamped on the output transformer... However it doesn't have the simul-class switch on the back of the amp. Is this 60/100 switch the same as the simul-class switch? Will it run just the outter two EL34's on the "60" setting, and all tubes on the "100" setting (two EL34's and two 5881's)? Do I need to re-bias the amp for the El34's? Also, is this amp set for a constant bias? In other words do I need to bias this amp?
I love the tone of this beast but would I like to try El34's in the outter sockets to compare tones.
Thanks in advance. Jeff.

 

[tony777]

As long as it have the simul class stamped or engraved on the output transformer, it is a simul class amp,
NOT a 60/100 watts version.
The amp cannot be both.
Simul class amps can have EL34's at the outer sockets, without doing anything with the amp.

To make things perfectly clear:
Does the switch say 60/100?
I have heard of a switch that say full power vs 1/2 power.

Pictures can tell more than a thousand words

 

[Generic Jeff]

 

[tony777]

So if it's engraved simul class on your OT it's a simul class amp, and you can have EL34's in the outer sockets.
If it's a black dot/no stripe (serial in th 15xxx range) it's a 75 watts at full power, and 15 watts at 1/2 power.

NB! if your amp has six 6L6 tubes it's a colliseum amp and EL34's have to be in the inner pair, and the wattage is insanely higher.

Rear view picture will do.

 

[MrMarkIII]

That is the Simul-Class switch. It's usually mis-labeled on long heads.
As a a matter of fact, I've yet to see one that isn't.
Switch down is 15 watts Class A. Switch up is 75 watts Simul-Class.
But you can't put EL-34s in the outer sockets of a 60/100.
Mesa amps' bias is factory set, so tell your tube supplier what you have and he can set you up with the right tubes - or use Mesa tubes. Sovtek 5881WXTs are pretty much the same as the old Mesa STR-430s afaik.
Try to find someone who will let go of some STR-454s (6L6), and STR-450s (EL-34).
Expensive, but da bomb.

 

[Generic Jeff]

SN is 158xx. Thanks gents for the informative replies. I'll be installing a fresh set of tubes (simul-class mix) in the near future. Great site btw.... Jeff.

 

[flip33]

Even at simul-class 15 watts the Mark III is insanely loud, e.g., loud enough for anything I want to play.

I can just barely tell the difference between 1/2 and full power.

 

[Generic Jeff]

I noticed it sounds a bit smoother or more compressed on the 1/2 power setting, though not much difference in volume at all.

 

[rvschulz]

I noticed it sounds a bit smoother or more compressed on the 1/2 power setting, though not much difference in volume at all.

well ... depending on the efficiency of your speaker and what you are doing with tone, 15 watts is not 5x louder than 75 watts ... not even perhaps 20% louder and only at REAL high volumes. you are noticing the difference - 15 watts breaks up earlier and ... it's where i live on my Mark IIIs. If I started playing insanely clean surf or country I might get the full power thing going.

and by the way, if you want to run 6L6 in the outers, you can. many like the EL34 in the outers and in the newer (green-stripe) it is more recommended - my purple-stripe docs do not even mention EL34. they run of course. i run all 6L6.

 

[MrMarkIII]

This is from a later, maybe green stripe, Mark III manual. This note does not appear in my earlier, 1990 blue stripe manual. The recommendation against 6L6s in the outer sockets was due to poor quality 6L6s in the mid-90s. It really no longer applies.

"NOTE: In the past, MESA/Boogie advertised the "interchangeable power tubes" feature of the Mark III Simul-Class. We told players
that they could use either EL-34's or 6L6's in the outer (Class A) power sockets. However, in recent years we've observed a much
greater reliability factor with the use of EL-34's in these outer sockets, with much fewer incidents of tube failure. Therefore, today we
strongly recommend using EL-34's in the outer sockets and 6L6's in the inner sockets of your Simul-Class Boogie."

It's harder to tell the Simul/Class A (15/75 watt) difference at volumes below 3.
Crank it!

 

[Generic Jeff]

I'm really digging the tone with a quad brew of 5881's through the lead channel. I'm thinking that the EL34's will give me more of a Marshall tone with the R2 channel. Hopefully the lead channel's tone will not suffer as a result.