Is my MKIII Combo overheating?

[Scott_hg]

I've been running my MKIII Blue Stripe Combo at gigs for over a month now. The first few gigs I was turning it off between sets but the last few I've left it on for the whole gig.

I noticed that in the third set my tone got a bit muddy and I wasn't cutting through and my volume was lower on the lead channel.

I suspect heat is causing this but has anyone else had similar issues? If so how did you resolve it?

 

[bandit2013]

I've been running my MKIII Blue Stripe Combo at gigs for over a month now. The first few gigs I was turning it off between sets but the last few I've left it on for the whole gig.

I noticed that in the third set my tone got a bit muddy and I wasn't cutting through and my volume was lower on the lead channel.

I suspect heat is causing this but has anyone else had similar issues? If so how did you resolve it?

Been there lots of time with the Mark III blue stripe combo. That was long ago when the Sylvania 6L6 and the RCA 6CA7 were available. I miss those days. Seemed like every three months of heavy use had to replace power tubes. It was usually the 6CA7/EL34 tubes that would go first. If you are running a quad of 6L6, the recommended tubes should be to use the EL34 in the outer sockets. There is an adendum that states that on the Mesa web site in the support section for the Mark III manual. It could also be a preamp tube needs replacement but my bet is on the power tubes. Here is the clause I found on the Mark III manual:

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.

 

[Scott_hg]

Thanks Bandit,

I don't have the simulclass version but I also suspected a valve issue - so I pulled them all out and inspected one by one.

I did note that one of my output valves was not pushed in all the way, that is now fixed.

I played a gig with the amp on the weekend just gone and had no issues at all. I did put a fan in behind it though just in case heat was the issue, but it ran like a dream all night long...

Scott

 

[bandit2013]

Good find, glad to hear you resolved the issue.

It has been a long time since I had the MKIII. Forgot they had some that were not Simulclass. Good that you did not kill the tube that was doing all the work. When one tube shuts down (due to poor connection, loose socket clip or not inserted all the way in, or could be internal fault in the tube) it generally sounds extremely distorted or very sic (not very musical).

 

[morgan138]

I played a gig with the amp on the weekend just gone and had no issues at all. I did put a fan in behind it though just in case heat was the issue, but it ran like a dream all night long...

Does your combo not have a fan built in? Mine has a hardwired one by the speaker, pointing right at the power tubes.

 

[Scott_hg]

Definitely no fan built in...

 

[bandit2013]

It has a fan, not a radial fan though, more of a linear motion type. That speaker will move some air on both sides so it helps to keep things somewhat cool as long as you are playing though it.

 

[woodbutcher65]

My Mark III combo came with a factory installed fan, installed below the top of the back (halfback) cover, blowing on the power tubes.

Just FYI, although they ARE rather pricey, Mesa still has some remaining stock of the classic STR 415 (6L6) and STR 416 (EL34/6CA7) Sylvania made (or Philips ECG) power tubes for those who are willing to pay 250 bucks for a pair of them. You just have to call and ask for them, they're not listed on the website as far as I can determine.

Tubes put out MORE power as they get hotter.

Generally the warning sign of things getting too hot is that if that happens, you'll smell it when you're close to the amp.

Ah the smell of a Studio .22 cooking itself to death after a long evening gig...I know it well. Those things were TERRIBLE about cooking themselves. Just bad thermal management design!