Using the MarkIV with 6V6 tubes and two cabs????

[mdortona]

Hi All!

Here's the story:

I recently popped in 4 6V6 tubes in my Mark IVA to tame things a bit volume wise and get a more Fender Deluxe-ish clean. I am following the customary instructions (i.e. Tweed power , Simulclass, plugging into the 4 ohm jack etc.). However, according to Markus at MB, running two 8 ohm cabs in parallel (in this case a MB EV-Theile and a MB open back cab) into the 4 ohm jacks with the 6v6s, isn't recommended. He suggested that I buy a series load box so that the amp "will see" a different, safer load. I'm still not clear why it should make a difference, since reportedly you can run a pair of 8 ohm cabs in parallel into the 4 ohm slots with the 6L6s without any issues. What am I missing or misunderstanding? Thanks in advance for the help and enlightenment!

Matt

 

[MrMarkIII]

The manual says to run an 8 ohm load into the 4 ohm jack. This "too high" mismatch is less of a load on the tubes so they won't blow. Two 8 ohm loads into both 4 ohm jacks just brings the total load back up to the nominal 8 ohms, not suitable for the 6V6s. Or at least they will wear faster and won't be covered under warranty.
Although... I wonder what would be the case if you ran a 16 ohm cab into the 8 ohm jack? Hmmmm...

 

[MesaDCLP]

I wonder what would be the case if you ran a 16 ohm cab into the 8 ohm jack?

+1

...or if two 8 ohm cabs were run in series?

 

[mdortona]

Thanks Mr. MarkIII, now that makes better sense to me Looks like it's back to the 6L6s for gigs and the 6V6s for special occasions :lol:

Matt

 

[MrMarkIII]

I wonder what would be the case if you ran a 16 ohm cab into the 8 ohm jack?

+1

...or if two 8 ohm cabs were run in series?

++1

... and if loudness is the problem, why run TWO cabs instead of one?
I've run the MkIV/6V6s into a EVM Thiele in a small rehearsal room (20 x 10) and it's still dang loud.
Mark IVs refuse to behave!

 

[ursinus]

I had a MKIV with 6v6's in it and I did exactly as MB said at Mesa Boogie. I used the serial box to make both 8 ohm cabs 16ohm and ran it into the 8 ohm outlet in the MKIV. When running 6V6's, Tweed is a must, so is doubling the impedance load. Maybe you can PM Boogiebabies for a more definitive answer.

 

[mdortona]

Thanks for all the advice and help!

Mr. MarkIII- I prefer to run two cabs to get the focus and bottom of the
Theile along with the air of an open-backed cab. I agree 100% about that running a pair of cabs being contradictory for someone looking to tame the volume on a MKIV. :lol:

I still may wind up going Ursinus' route with the load box, as MB recommended, but the jury is still out. Ursinus, did you notice a minor gain reduction on R2 using the 6v6s? I gigged with the 6v6s last night and the amp didn't seem, to have as much "punch and crank" like before with the 6L6s. Then again it could be my imagination :wink:

Again, I really appreciate everyone's input

Matt

 

[ursinus]

On the contrary. With 6V6's, I got more bass and gain. I had to lower the bass on the eq and lower the gain on the lead channel. R2 became perfect with the 6V6's. The clean channel also benefitted with the 6V6's. it sounded much more "bubbly" and "3D"

BTW, I preferred the Electro Harmonix 6V6's from Doug's tubes. Make sure you tell him its for a Mesa MKIV and he'll set you up. The Mesa labelled 6v6's were ok, but not as rich sounding.