# Tube amps - How hot is too hot?



## soldierscry (Jan 20, 2008)

I have own a number of different tube amps (both head and combos) over the years. I know that tube amps get hot, but recently since I have been jamming more i noticed that my Measa ED combo is so hot by the end of the jam (2 to 3 hours) the chassis is too hot to touch which I have never really noticed with my other amps over the year. It got so hot one jam that one of the cables in the fx loop to fail. 

The amp is under warranty so I had L&M check it out and they reached out to Mesa. Mesa says that it is normal and that the ED tends to run hot but would not provide a safe operating temperature for the amp. So I got a hold of a Temperature gun and decided to see how hot it was getting as L&M didn't have one.

Setup 1:
Guitar into amp
CE-2 in the FX loop
Rockcrusher between the amp and speaker

Setup 2:
Guitar into amp.
nothing in the loop
no Rock crusher used

Both tests produced similar number as below

Results after a 2 hour jam (Temp is in Celsius):
Front panel: 60
Back panel: 81 

I know that it gets even hotter after a 3 hours but I didn't having it running that long this week.

Just wondering if anyone has seen this before as i know there are a few ED owners on here as well as some very knowledgeable people how might be able to provide insight.

I am wanting on a call from a Mesa tech to discuss the issue. So I will update after I talk to them.

Thanks


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## dcole (Oct 8, 2008)

To me that seems a tad ridiculous. Maybe it needs a fan drawing air across the output tubes?


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## soldierscry (Jan 20, 2008)

A Fan would help forsure and Mesa mentioned that to the Tech at L&M but also told them if the amp is modified for a fan it would void the warranty. I could always make a little mountable fan the can run of a 9V Power supply. I afraid adding a fan to keep things cool is potentially just going to mask the real cause of the problem if there is one.


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## Scotty (Jan 30, 2013)

That seems crazy hot. What "should" it be? 

Generally speaking, do tubes run hotter when the amp is driven, or do they normally hit a peak temp and stay there as long as the unit is on, regardless of amp volume/gain levels?


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## soldierscry (Jan 20, 2008)

I asked that and Mesa wasn't able to provide an answer which is why I did the tests and had L&M send the the results. Mesa is going to try to repeat my test and see what results they get.

For reference these are my amps settings.


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## dcole (Oct 8, 2008)

Oh, this is a small combo amp with a 100 watt tube amp shoved in the back of it? I would expect higher than normal chassis temperature then. There is a lot of heat given off by vacuum tubes, not only the heaters themselves but the plates as well of the power tubes. Heat rises, in this case, straight into the chassis.


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## mhammer (Nov 30, 2007)

Didn't older Mesa amps include fans?


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## soldierscry (Jan 20, 2008)

mhammer said:


> Didn't older Mesa amps include fans?


I believe so. I know they put a fan in the lonestar specials


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## PTWamps (Aug 5, 2016)

mhammer said:


> Didn't older Mesa amps include fans?


Yes, I've seen a couple of 80s/ 90s Mesas that had those little black box fans, like you find in computers. Those can be bought and installed pretty easily if you know how to take a feed off of the AC supply in the chassis.


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## mhammer (Nov 30, 2007)

Just be sure you're not trying to feed a 12VDC fan with 120VAC!


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## Lemmy Hangslong (May 11, 2006)

Yeah that's a hot one for sure. But as for safe operating temperatures I would look to the Transformer Specs first and the wiring next. You will likely find that both are good for at least 90 degrees Celsius possible higher. Many Marshalls run very hot as well. My old 69 Plexi gets very hot by half way through a gig. In fact it has charred wood and tolex above the power tubes that clearly show it gets very hot. There is actually a strip of asbestos there to protect it. In the winter venues have the heat on and in the summer venues have the air conditioning on which really makes no difference as they are trying to maintain a comfortable temp usually around 18 to 22.
As for your effects loop cable that failed... did it melt? Most are cables are rated for at least 75 degrees Celsius so may be 90.
I wouldn't power a fan from the DC power supply of the amp that can cause other issues. I suggest that if you are concerned about the heat damaging your amp or cabling or getting a burn, run a AC plug in fan behind the amp blowing directly at the heat source. That's what I do in the summer at gigs where it's way to warm and with no AC. I don't have any noise issues at all from the fan.


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## Chito (Feb 17, 2006)

My Peavey Classic 30 is the same thing. It gets so hot you can't touch any of the metal parts. But it's a known thing with the C30. I guess what I'm trying to say is, it probably takes a lot more higher temperatures before it becomes an issue with the amp.


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## soldierscry (Jan 20, 2008)

dcole said:


> Oh, this is a small combo amp with a 100 watt tube amp shoved in the back of it? I would expect higher than normal chassis temperature then. There is a lot of heat given off by vacuum tubes, not only the heaters themselves but the plates as well of the power tubes. Heat rises, in this case, straight into the chassis.


You are correct it is the small combo, which I expected to run a little hotter.


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## dcole (Oct 8, 2008)

mhammer said:


> Just be sure you're not trying to feed a 12VDC fan with 120VAC!


Why not the B+ inside the amp? That would really get things moving, lol!


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## GUInessTARS (Dec 28, 2007)

I have a Mesa Mark IV that melted a curtain on stage. The curtain got pushed over the back of the amp sometime during a 45 minute set,
and was thoroughly toasted. The amp performed perfectly, I never noticed the problem until we were packing up.
Used the same amp and tubes for the rest of the year, at least 12 more gigs. Amp is still working fine (have changed tubes since), that was 20 years ago.


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## PTWamps (Aug 5, 2016)

mhammer said:


> Just be sure you're not trying to feed a 12VDC fan with 120VAC!


The ones I've seen are clearly labelled 115VAC or 12 or 24 VDC. Search | KGE électronique

No-brainer for anyone able to hook one up in the first place.


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## High/Deaf (Aug 19, 2009)

Scotty said:


> That seems crazy hot. What "should" it be?
> 
> Generally speaking, do tubes run hotter when the amp is driven, or do they normally hit a peak temp and stay there as long as the unit is on, regardless of amp volume/gain levels?


Class A/B amps (which are about 98% of the amps out there) get hotter as you run them harder. And cool when you idle them for a while. But when they get hot, much of that heat is maintained in large metal lumps (both transformers). They take a while to get really hot, and they take a while to cool down as well.

Class A amps, by design, dissipate as much heat idling as at full gate. But they are usually single ended, low power amps and you don't notice it so much. Large class A hi-fi power amps rally show this tendency. My LSS is Class A push/pull (quite uncommon as it's very inefficient) has a fan inside for that reason. Of note, the fan does not point directly at the power tubes but at an angle, circulating the air around the inside of the cabinet. They apparently don't want hot spots and cold spots around the power tubes.


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## helliott1 (Jul 12, 2015)

Silly question maybe, but ... You are putting it on standby whenever you break for more than a minute or two? My Mesa LSS gets very hot after a one-hour set, but cools off in a 20 minute break on standby. But it also has a built in fan so that may not be a direct comparison. Use standby when you can though.


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## High/Deaf (Aug 19, 2009)

Yes, standby does allow the amp to cool. If you just leave it on and don't play it for a while, it stays just as hot as if you were pegging it for that time. The fan has a switch but that's apparently if fan noise is bothersome in a studio. They don't recommend running it for long with the fan off.


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## bolero (Oct 11, 2006)

I had a little Garnet tube combo that overheated once...the drummer stuffed a shirt in behind/over the back of amp while I was playing, without my knowledge

after an hour or so the amp started cutting out, I looked behind it WTF!

after I removed the obstacle & it cooled back down, it worked fine though. you could have fried an egg on the thing!


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