How's the cooling capability?

[GJgo]

Hey guys,

Looking at a few things, wanted to air a thought. The JP-2C is compact & dense. It has a smaller fan that flows less air than the earlier Mark amps. Has anyone considered if it makes sense to open up the front or something to promote more airflow through the chassis? Is anyone concerned about heat management with this design?

 

[Markedman]

I'm not worried in the least, the guys at Mesa/Boogie know a thing or two about how much heat is desirable for this amp.

 

[bandit2013]

Perhaps I am wrong about this but here is my take on it..... JP-2C does not seem to get overly hot as it is a class A/B power amp. If Mesa had stuck to their plan with the fixed bias method as they do with the other class A/B amps all will be good. That small fan is enough to allow the cabinet to breath. I have spent hours on end playing though the JP-2C an have not noticed overheated chassis. Amp stays cool, tubes are hot but they always will be.

The early marks were different, some were class A/B and some were Simul-class. In my past experience with Mark III, Mark IV and Mark V all having Simul-Class power section, runs much hotter than the Class A/B. Also if the amp had EL34 capabilities, those tubes run much hotter due to the smaller tube size and high plate voltage.

 

[GJgo]

That's a good observation, thanks Bandit. My JP feels like it runs hotter than my Mark III, but the III has a big fan. Time will tell I suppose.

 

[elvis]

I run the JP cranked up pretty good while on a tight shelf against the wall. I left room for airflow, but it is not ideal. I guess I'll find out, but it gets nowhere near as hot as my Dyne.

 

[Markedman]

My Mark llC+ 60 watt 2X 6L6 didn't have a fan.

 

[bandit2013]

The obvious observation: it is a tube amp. Of course it will get hot. but how hot is hot?
When I first got my Mark V as a head, I could not believe how hot the chassis was getting. Hot enough I could not touch the chassis. The PT was as hot as the tubes. Also I was having issues with the amp red plating tubes at that time. Mark IV combo would get hot but it paled in comparison to the Mark V as it had a larger 120vac fan blowing upward from the bottom of the shell. Also the speaker helped with air movement considerably. I had my reasons to convert the Mark V to a combo and since I have done so it does not soak in the heat anymore. Before I modified the bias (not by much mind you) I could only run SED =c= tubes in the amp as those were the only one's that would last more than 8 months. Mesa tubes (average life span was 2 months or less).

Roadster head has no fan, but the tubes are not hanging below the chassis, they are pointing up. I wanted the version with the Road king faceplate as that had a grill on the front. Amp has a grill on top just above the power tubes. I would say this one stays much cooler than the Mark series amps that have the sinul-class power tube circuit. Also running temperatures of the Roadster (along with the 4x6L6GC it has two Rectifier tubes that contribute to thermal radiation) is comparable to the JP-2C. Chassis may get a little warm. Speaker wires stay basically at room temperature (the Mark V was cooking the speaker cables). I did borrow a IR meter to measure the temps long ago, will have to dig for that info as I think I compared the radiated heat of the Mark V to that of the Mark IV but may not have posted the data.

On the flip side, I have a Carvin V3MC that has a quad of the EL84 tubes. Also has an adjustable bias. When I first got it, that sucker cooked and was about the same as the Mark V. I checked bias and it was set too high. After adjustment all it does is get warm but still would not touch the tubes as those little EL84 will definitely burn you even with gloves.

What it boils down to is this, how hot are the internal components getting? I am not worried about the tubes but the other components like resistors, relays, transistors (most of which will be fine at elevated ambient temperatures) and finally electrolytic capacitors (most susceptible to heat). Perhaps the worry is just that....My Mark III lasted for 23 years without any issue and it is still going strong as I know the person I sold it to.

 

[elvis]

Well, in the end, heat is bad for components, as you mentioned, and should be minimized where possible. I prefer a chassis where the tubes are on top. Unfortunately, the JP is not such a chassis. The fan should help move a lot of the heat out, even if it's a little fan that doesn't move much air. But heat rises.

Bottom line - the amps will need service every couple of decades for best results. I can live with that.

 

[GJgo]

I may just roll without the front cover screwed in most of the time. Easy to R&R, and it'll let it breathe. It may not do anything but make me feel better, but hey..

 

[bandit2013]

GJgo,
Are you experiencing a hot running chassis? Is the power transformer hot enough to burn you? I will try to borrow a thermal probe from work to see how hot mine is getting but at the moment it remains just warm and does not seem to be a concern of mine. With the face plate removed, that will change the air flow characteristic of the fan. Since it is mounted at an angle to circulate air within an envelope, some outside air is pulled in as some is pushed out since it is a closed end box with one side open. Removal of the face plate will limit how much air passes out and one side may get hotter than the other. One would hope that air flow modeling was performed in the design of the chassis and enclosure to ensure good air flow around the tubes. Unfortunately, it is just a small box fan that can recirculate air from exhaust back to inlet as there is no air baffle to prevent back feed. When I run my JP-2C, I can go for several hours as it is hard to stop. I have yet to experience the super heated chassis like I have with the Mark V. I also have a RA100 (actually two). The head version had a rear cover that basically reduces the opening considerably on the back side of the amp. The small 2 speed fan basically pushes air over the power soak resistor but also helps keep the rest of the amp cool. However, I have removed the rear cover while I was tube rolling and noticed a difference as it seemed the amp got hotter with the cover removed, also the metal grill effected how the air flow passed within the cavity. Yeah, this one has a top grill too but I had better thermal performance with the amp with cover in place. Combo's can be excluded unless the speaker is sealed (Roadster combo) as they move more air than the fan (this applies to the Mark III and Mark IV combos).

If you are having heat issues, you have two options, contact Mesa Customer service and report the issue, and secondly, replace your power tubes as you may have one that is not matched or is out of tolerance. One way to find out what may be causing it, turn the amp around facing away from you, remove the grill and turn the lights out and play. If you notice the seams on the plates of the tubes turning cherry red but the rest of the plates are dark there could be something out of its performance spec within the amp or it could be the tubes themselves. Note that if you are pushing the envelope (high volume) it is possible to get the tubes to glow slightly (this is my experience with the simul-class circuit : Mark IV, and Mark V). I have yet to experience this with a Class A/B circuit as all the tubes are running at the same bias. The chassis will get warm but should remain below 180F (assumed, based on UL requirements for exposed metal parts that can be touched by hands, also this was the thermal limit for operating temperatures of electronic products that I have personally worked on in design and development). Also note that the chassis does not seal at the top of the shell in front, along the sides and on the rear as it does have an air gap to allow for heat dissipation.

What is your speaker load? That may also play a role in operating temperature....always best to match load to output. At least you have 3 options with the JP-2C. 16, 8, 4.

 

[SamuelJ86]

I wanted to add my experience on this topic. The temperature my amp runs at doesn't concern me. I enjoy touching the giant transformer after playing. It's hot but not burning hot. Same with the chassis. Also the smell from inside the amp is very pleasing, but that's neither here nor there. But I have had one hiccup with my amp involving temperature. And it wasn't necessarily the amp, it was the built in cab clone. The first time I tried out the headphone out of the cab clone my amp shut down. I was using my audio technica m50x. I wasn't getting enough volume for my liking, I like it loud, so I had to run the master at 2 o'clock to get the loudness I wanted. The amp shut down after about 20 minutes of that. The chassis beside the cabclone was too hot to touch. The attenuation device in the cab clone probably had all it could take as 2 o'clock on the master with my settings is freaking loud. And that is a ton of energy that has to be bottled up by the cab clone and dissipated into heat. I believe the RA 100 has a similar attenuation device, but it is mounted outside of the chassis and has a faster fan blowing air directly on it. On the JP2C, it is mounted inside the chassis, where there is not much airflow.

So that is a concern, at least for me. Even though I don't use the cabclone for anything but the headphone out, when I do, I have to keep in mind that all that energy that is usually being used to drive my speakers and shake my house is being turned into heat inside the chassis with minimal airflow and important components all around. So I would recommend all the cab clone users to be aware of this.

 

[bandit2013]

That is good to hear Samuel, or is it :| How does the cab clone sound with the amp at 60W? At least you can reduce the amount of power in the large resistor inside it. I also noticed only a small air gap around the chassis and top of cabinet. RA100, and Mark V both have vents on the back side of the chassis.

I guess I am happy I have a reactive load box then. Have not used it with the JP-2C yet.

I had played the JP-2C for a while, about 2-3 hour without stopping. Was thinking about this thread and well, chassis just above the tubes was warmer than the rest, hard to say hot as I was able to hold my hand there without getting burned (would be great as a hand warmer on a cold winter night though. The power transformer was cool, still at room temperature. Perhaps I do not play loud enough....... :roll:

 

[SamuelJ86]

Interesting bandit, I wonder why mine is running a bit hotter than yours. I felt it up again tonight :lol: I like your hand warmer idea, that's about what my transformer feels like after playing, about the temperature of a hand warmer, or comfortably hot. The chassis above the tubes is a bit more hot, maybe too hot for hand warmers.

I wonder if my power tubes could cause that. I'm using mesa str 415's. You're a bit more knowledgeable in that department than me, what do you think? I run the master at about 11:30. Settings are in the ballpark of JP's from the manual. It never gets burning hot, even after running the master at 2 o'clock. It's comparable to my mark V so no worries.

 

[bandit2013]

Tubes could play an important role in the heat dissipation. Yesterdays tubes may need a different bias compared to what is used now. It all depends on what the color codes are on the tubes. (assuming that was used then). The STR415 is quite different than the more recent STR440 so the construction, heater core, cathode doping, type of glass, and plate material will all contribute to the thermal characteristics, along with a different bias point (assuming that the STR440 may be different than the STR415 but probably not by much.) Common issue with fixed bias amps, not all tubes will behave the same as the bias points are usually different depending on the model of amp you are using. Rectifiers run cold, Mark V runs hot (inner pair, or which ever pair is used at half power vs full power in simul-class amps). If the STR415 are on the hot (early gain) side of the distortion range, they will dissipate more heat if they are drawing more bias current. If you had a set of colder tubes, you would probably have more headroom, less gain characteristics and cooler operating temperatures. There are so many variables at play so it is difficult to narrow down root cause of thermal generation that may be of concern other than the power tubes being the main contributor. Preamp tubes also add to the heat but not as much as the larger bottles.

Then comes the question to mind, is the fan running at is intended speed? Is it even running?

TMI portion of my rambling.....
After my experiences with the Mark V, I have been made weary on tube life, that amp would run close to red-plating (before I altered the bias point with a change in bias resistor). Before the mod, the amp chassis got so hot I would not dare touch it or I would get burned. Power transformer also cooking. When I hit a power chord (even with variac power) I could see the seams on the plates turning cherry red on the center pair of tubes. Mark IV would do the same at insanely high volume levels but all tubes would get that 6V6 glow. JP-2C, hard to tell if the plate seams are getting too hot. I sat there in the dark watching the power tubes for that effect, all I could see was heater glow and the ghostly blue hue dancing on the glass. More fun than a barrel full of monkeys might I add. Never noticed a sliver of orange on the plate seams that I could see. (other side of the tube could be the side getting cooked and it all depends on where the grid voltage gaps are.)

One more observation: Both the Roadster and JP-2C are the only two amps I own using 6L6GC tubes that do not have tube rattle. Mark V I can hear the tubes singing away and sometimes I get that rattle sound. More noticeable if I use the combo speaker, but it is still there using an extension speaker that the amp is not sitting on. I have used the same tubes in my Roadster and the rattle is not apparent. RA100, different story, EL34 always make noise except for the Mullard re-issue versions.

 

[GJgo]

Alright, for curiosity's sake I got out my infrared pyrometer tonight. I played for about 20 minutes with the speaker off, cab clone through my headphones, in 60 watt mode with the volume at noon. The hottest part of the chassis was the right side (looking from the back) at about 150°f. The outside power tubes were running about 275°f. Afterwards I turned the speaker back on (but did not play, kids asleep) and let it set for about 10 minutes, and when I checked again the chassis was about 125°f and the power tubes were about 250°f. I'll keep tabs on it during more play time. The power transformer never really gets that hot, I agree maybe hand warmer temperature.

Update, tonight I played through a speaker in 60w mode with the volume at 10:00 for about 20 minutes. The temp on the rear right of the chassis was 95°f. Way, way cooler than with the CabClone running & speaker off.

I'll compare to my Mark III as well.

 

[bandit2013]

If it was mentioned before, using the cab clone with the speaker off will divert the load current through a resistance load mounted on the chassis. That will definitely add heat to the chassis as most of the power is dissipated in the form of thermal energy. I have not considered the cab clone to be the issue as I have not considered trying it yet. I doubt that I would ever use it with the speaker off.

Some good points in this thread. I scanned the section of the Cab-clone in the manual, does not make any mention or notice about cooking the chassis when using the speaker off switch. What would be needed, large heat sink with attached mini fan to keep things cool (similar to a CPU fan). Doubt there is any room to fit in the chassis.

 

[GJgo]

I never heard back from Mesa on my question I sent them. At any rate, tonight I played the same way w/ CabClone and I just got a desk fan & pointed it at the back side of the chassis where it gets cookin' hot. Made a massive difference to the surface temp, temps felt more like my Mark III with the big fan. I'm just going to do this when cab cloning.

 

[GJgo]

So I was chatting with Mike B. about another amp I sent him for service & I floated him this temp question, he told me that the temps I measured on the chassis were "awful dang hot" and he though the extra fan when playing in CabClone with the speaker off was a good idea. That's enough for me.

 

[bandit2013]

I would agree, high temps that are beyond expected ranges are not good for the circuits inside. An additional fan will help some, but not as effective if the thermal energy cannot be removed from inside the chassis. Perhaps if the head had a top vent like the Rectifier amps or the Royal Atlantic. Note that most passive components will be fine at elevated temperatures if they are so rated for that type of service, however, solid state components like processors (midi controller), and most transistors (JFETS, MOSFETS and BJT's ) do not favor high temperatures and usually lead to failure or poor performance. Too bad this was not taken into account for silent use with headphones using the cab clone. The load resistor could have been mounted on the underside of the chassis for improved thermal dissipation similar to the RA100 power soak resistor but would have taken up real estate on the chassis where the preamp tubes are located. Perhaps a vented chassis with a heat sink would have helped so some degree. I wonder if the engineer took into account the added thermal stresses to the internals due to the loading of the load at 100Wrms+ (found to be around 148Wrms) as the peak power is higher on the JP-2C that what I found from the RA100 or the Roadster (never went above 100Wrms). Even the Mark V peaks at 110Wrms ( a bit higher than the 90W nominal). If I want to get the true facts I could borrow one of the oscilloscopes that I work with that can measure peak currents. So tempting to borrow it along with the current probes as that would be cool to see real data vs something that is probably not calibrated (Rivera Rock Crusher recording attenuator).

Definitely and opportunity for improvement. Perhaps if the Cab clone was fan cooled would be ideal for extended use with the speaker off. Makes me wonder if the rack mounted version has similar heat issues.

I have yet to use the cab clone so my experience is limited in that regard. I know it is there but not something I need or would use but that may change once I take the time to try it out.

 

[PBGas]

Interesting to hear this. I really don't use the Cab Clone myself as I have a Torpedo Studio. Still, have to keep an eye on things if I ever do use it.