The Mark V head runs very hot !, is this normal?

[bandit2013]

This amp can get very toasty. Seems to be alot of heat soak in the chasis (probably to to the power transformer) I let the MKV warm up while I was playing throught the MKIV combo. The MKV was in standby for at least 2 hours by the time I got around to playing through it. The front of the chasis was almost too hot to touch but not hot enough to cause any burns. Played through the MKV for at least 3 hours. Yippy, all the tubes are still working. However, 2 hours after shutting down the amp I noticed the chasis was still quite hot. The tubes were almost at room temp.

I was considering popping out the rubber plugs on the bottom of the chasis, Open up the panel in the front behind the grill and adding a low to mid RPM fan onto the back of the amp to draw air in from the front and pull out to the rear. I am also considering adding an openinng with a grill on the top of the amp behind the handle. I expect there will be some heat due to the nature of the amplifier. I just want to make it breath better. The fan in the MKIV is much larger but makes more noise but the amp stays a bit cooler.

Any thoughts about adding ventilation or an additional fan to the MKV?

 

[screamingdaisy]

Personally, I've always felt that Mesa intentionally heats up the chassis on the Mark series. The few Marks I've owned have always sounded better once they start getting hot. I figure it's a big part of why every Mark or Mark derivative has always been tubes down regardless of whether it's a head or combo version. Switching heads to tubes up would save Mesa money since they wouldn't need the fan or the heat sink.

That said, still being hot two hours later seems a little odd. I currently own a Mark V and don't remember it running any hotter than previous versions.

 

[bandit2013]

The filament transformer I believe is the heat source. It takes a while for the iron core to cool down.

 

[farren]

I don't have much of a clue as to what is "too hot" for a tube amp, but perhaps a product of my obsessive PC/AVR cooling, I decided to mount a very quiet under-volted 200 mm fan on my cab perpendicular to the back of my Mark V head (the length of the fan running from the back of the head shell to the wall behind my half-stack.) Peak temps as measured with an IR thermometer went from 125 F (highest when aimed at the power tubes) with the stock fan enabled to 110 F with the 200 mm fan only. Due to turbulence, I suspect, temps went up slightly (~5 degrees) when I used both the stock fan AND the 200 mm together.

Was 125 F too hot? I don't know, but the new fan is much quieter than that 1.5A buzz-saw A 200 mm 5-12 volt case fan will run you $12-15 and a typical stand-alone AC to DC 5-12 volt adapter $15-20, which often come with molex to 3/4-pin adapters for powering fans. 2A is plenty for the adapter.

 

[dino2sf]

If you decide to open up the area behind the grill you will be able to change tubes very easily. You would have to remove the grill from the grill piece and drill holes in it then put the grill material back on. The piece is solid wood and wouldnt let air through if you didnt. At home I usually leave the grill off so I get lots of airflow. Super easy mod to do ...see my thread regarding cutting out the wood behind the grill.

http://forum.grailtone.com/viewtopic.php?f=33&t=63388

 

[bandit2013]

If you decide to open up the area behind the grill you will be able to change tubes very easily. You would have to remove the grill from the grill piece and drill holes in it then put the grill material back on. The piece is solid wood and wouldnt let air through if you didnt. At home I usually leave the grill off so I get lots of airflow. Super easy mod to do ...see my thread regarding cutting out the wood behind the grill.

http://forum.grailtone.com/viewtopic.php?f=33&t=63388

Yep, I saw your thread before posting. I am still debating on doing this. My concern is not the temps within the envelope of the shell below the chassis, of course the tubes contribute to the thermals. However, I am concerned with the temps withing the metal chassis. Capacitors, resistors, relays, etc... have operating limits. Overheat an electrolytic capacitor long enough it will degrade rapidly. The chassis gets very hot almost to the point it is softening the insulation on the speaker cable. If there was a way to efficiently allow thermal release in the chassis I would consider it.

As to the temps (unknown), the only meter I had at the moment are my fingers. My MKIV under the same operating conditions does not heat up this much (have to consider there is a large cooling fan in the enclosure), I could borrow a pyrometer from work to get an idea. Too bad the thermal image scope I requested at work was placed on hold, that would definately identify the hot spots. If we ever rent one again, I will have to scan the amp just for curiosity.

As for taking temps of the tubes themselves, you would almost have to paint them flat black to get a reasonable measurement using an IR pyrometer. The emmissivity of the glass along with other shinny objects will through off measurements (however, readings do have some merit but they will not be precise so ball park is okay).

 

[farren]

As for taking temps of the tubes themselves, you would almost have to paint them flat black to get a reasonable measurement using an IR pyrometer. The emmissivity of the glass along with other shinny objects will through off measurements (however, readings do have some merit but they will not be precise so ball park is okay).

Yeah, I don't put that much faith in the precision of my readings. I basically sprayed about for a few minutes looking for an general average and a high. I'm quite sure the new fan is an improvement, though.

 

[bandit2013]

Update on Easy Bake Oven issue;
I did a complete retube of the amp. I can now play through the amp as long as I want to without the amp getting as hot as it did. The filiment transformer does not heat soak as it did before the retube. The only original tube that remains is the rectifier. I was considering adding a fan or cutting out the front panel, does not seem necessary now unless I want easy access to replace preamp tubes ( I do not expect to do that often.)