Mark-4 Questions

[Allegron]

Hi All. I Recently joined this forum ,and am looking forward to gaining insight regarding Mesa products that many of you have knowledge of. I currently own a Simul-class 2:90;a Recto Recording Pre-amp; two sattelite cabs with Tone Tubbys; and a Mark-4. (1991 I think) I'll start by asking a few questions regarding the Mark-4.
1: Does anyone know what the 1/4 inch jack on the chasis near a transformer is for? 2: I never understood why Mesa put two 4 ohm speaker jacks next to the 8 ohm jack for the internal 12 inch EV.What should I do to use my 8 ohm sattelite cabs as extensions to the Mark-4?
3:When I'm in "Tweed" mode I notice buzzing/hum; When in "Full Power" mode the noise drops off considerably. Is this related to the fan?
I haven't changed tubes in quite awhile,but after I replace a couple pots and the rotary mode select switch, I'm re-tubing the amp.(Svetlana 6L6s and JJ 12ax7s from Eurotubes.) Thanks for any info, Allegron.

 

[lockbody]

Regarding the speaker outs: If you run (1x) 8ohm speaker, you should plug it into the "8ohm" out. If you run (1x) 4ohm, or (2x) 8ohm, you should plug into the "4ohm" out(s).

 

[t0aj15]

deleted

 

[Shep]

that isn't the right mannal.......you have a mk ivA.... the 1/4 jack is a send to your satlite amp..it switchs the EQ on and off..so if you switch your eg off on your amp it switch the eq off on the satelite...

 

[Allegron]

I contacted Mesa Tech Support yesterday to order some parts and regarding my three questions: 1: Yes the 1/4 inch jack on the chasis is for EQ switching a sattelite cab. 2:Regarding the two 4-ohm speaker jacks: Of course you can hook up two 4-ohm speakers but in the case of using 8-ohm speakers: plug the internal 8-ohm EV into the first 4-ohm jack, then plug in an 8-ohm extension speaker into the other 4-ohm jack. 3: They told me- to find out where the hum is coming from: Diconnect the fan;try swapping out tubes etc; the process of elimination;maybe a tube problem... Anyway in the near future I'll try this process. Allegron.

 

[lockbody]

Of course you can hook up two 4-ohm speakers ...

I don't think I'd run my MK IV with a 2ohm load.

 

[Russ]

If you like having your Mark IV up and running do not use 2 cabs that are 4 ohms each into the 4 ohm inputs. The amp is not 2 ohm stable. You will want to use the 4 ohm jacks for running a pair of 8 ohm cabs or the internal 8 ohm speaker and an extension cab of 8 ohms. Also, it is not a good idea to run the internal speaker and a 4 ohm cab. I think that it would be nice to be able to run a pair of 4 ohm cabs but that is asking a bit much. It would have been nice if they had designed it to run the 8 ohm load as a pair of 16 ohm cabs though. It kind of limits you to your speaker cabinet choices. I think this may be one of the few faults of the Mark IV. I prefer my Marshalls for this point. But then again, a JCM800 and a JMP are hard to contend with anyway.

 

[SeasonOfPain]

What about plugging the Mark IV's two 4-ohm outs into the two 4-ohm inputs on a Mesa Standard 4x12? I can't remember how the wiring works on that cab.

I can't think of a particular reason for this (any advantage over the single 8-ohm?), more curious than anything.

 

[Russ]

I believe that still presents a 2 ohm load that you cannot support with the Mark IV or many other amps for that matter...