So you wanna run your Mesa Walkabout Scout at 2, 2.6 Ohms?

[MuthaFunk]

After reading about other TBers using their Mesa Walkabouts at 2 Ohms without any problems I picked up a local Scout combo with the intent of running a 4 Ohm extension cab I already have. Once I got the combo I couldn't help myself and had to remove the amp from the combo just for kicks. I was quite surprised that buried in the combos chassis was a handle attached to the head for when the head is removed. Nice touch Mesa!

What surprised me and what I didn't like was the lable seen below:





Here's what it looks like with the cover on:



And here's with the cover off:



That's a lot of venting they are covering up with that back cover!! After I ran the amp at 2 Ohms carefully for a practice, I monitored how the heat is dissipated throughout the amp. I know from my electronics background that you can squeeze a little more head room out of SS amps if you keep them cooler. I found a few flaws in the Scouts design IMO. The stock fan Mesa choose is capable of moving much more air flow than the exposed vents can vent. I believe there is a slight positive pressure buildup of air in the amp because of this and thusly makes the fan a little noisier than it has to be. Those of you who installed a quieter lower volume fan will most likely still achieve the same cooling of the stock fan despite the lower volume rating of the new quieter fan due to the limited vent holes.

The heat sink side of the amp is equipped with much vent holes on the side of the amp as well. With the cover in place the heat dissipated by the air moving out the of the side of the amp is directed on a long natural heat opposing down direction to be dispersed right at the fan intake, recirculating heated air for cooling. Heat rises.... This could have been designed a little better by Mesa. Perhaps some side vents at the top back of the combo would better vent this heat out of the combo away from the amp.

I read about the preamp tubes sounding a little more dirty when they get heated up on a long gig. I have devised a cheap solution to these heat related problems that probably only show up when the combo is ran below 4 Ohms. It will ensure an even longer life of the Walkabout amp while spending it's life mounted in the Scout combo as any reduction in heat absorbed by the internal components will allow a longer service life.

It started with a trip to the Home Depot where I bout a 8' piece of U channel for $5 and some door weather striping for another $3. 1 Hour later I had made 3 of these up:









My plan was to use these to hold the amp in place instead of the vent covering wood. I wish I could have found the silver aluminum U channel but the Gold was all they had in stock. The gold aluminum is actually lighter than the wood cover so I actually reduced my Scouts weight as well!

Here's the installed pics:







I haven't used it on a gig yet but I can tell you there is much more air movement and all the heat is dissipated out of the amp and away from it. The real benefit here is allowing the heat sink side vents to vent vertically out the top of the combo and not out the bottom to be pulled back in by the fan. I believe this will give me a much longer service life of my Walkabout amp as opposed to having the cover installed.

[12bass]

Nice!

[finalrequiem]

I might do this just because. I don't even have an extension cab at the moment but it would be cool to have those handy, just in case.

[Chef]

Alternatively, you could cut vent holes in the back panel.

Nice job though; i'm sure it helps.

[MuthaFunk]

Originally Posted by Chef

Alternatively, you could cut vent holes in the back panel.

Nice job though; i'm sure it helps.

I thought I'd try to keep my mods reversible until I know for sure this Scout is a keeper. If I find I'm running it without the extension cab all the time, I'd like to go back to the cover just because it's a cleaner look IMO.

[BillyB_from_LZ]

The latest version seems to be the first style of Walkabout to have a ventilated top. The two that I've owned were both solid top with marking either. When the Scout combo cabinet was designed, the amp had a solid top so the air vents out through the holes in front and the sides of the chassis and then down through the holes in the cabinet on either side of the amp.

[Chef]

Yessir, I noticed that too.
I don't think my black-face has top vents like that...

edit after a look-see at mine unit, and, paperwork:

My blackface was shipped to me on 5/27/09; no top vents that I can see thru the headcase.

Can't see my serial thru the headcase.

[RickenBoogie]

Nice work on those rails, looks pro. My '06 model has no top vents either, but I dumped my Scout cab long ago.

[Johnius]

I would like to see a Mesa rep jump in here. The concerns you have addressed are valid and important. I got my Scout Combo back in August. I will take off the back cover tonight to see what's up. I really like that amp; I'd hate for it die young because of a design flaw.

[Jazzdogg]

I'd be interested in seeing a response from a Mesa representative on this topic.

[Chef]

I've never seen Mesa employees on TB.

[ishouldbeking]

FWIW, the above issues may be real, but I've yet to hear a confirmed report of an overheated Walkabout. the guy at the mesa store mentioned that running them at 2 ohms can lead to thermal shutdown, but he didn't say he'd personally seen it happen, and I dont think anyone on TB has ever reported it happening either.

Hopefully this redesign has more to do with Mesa being overly cautious and doesn't reflect some change in internal components that requires more cooling..

[P. Bass]

Another consideration re overheating is w/ the speaker voice coils. Since a 4ohm speaker coil runs hotter than a 8ohm @ the same volume, I wonder how the coils will stand up @ 2ohms?
B.

[vin*tone]

The impedance of each speaker is still 4Ω but the amp only sees 2Ω bc they're wired in parallel.

[P. Bass]

Originally Posted by vin*tone

The impedance of each speaker is still 4Ω but the amp only sees 2Ω bc they're wired in parallel.

Understood. Thanks.
B.

[MuthaFunk]

I don't think anyone has toasted their Walkabout to the point of damage yet. I think Mesa recommends 4 Ohm minimum to combat the poor cooling design in the combo. I'm just making improvements to help lengthen the life of the amp and allow it to weather the abuse I know I'm going to subject it to.

[MattyH]

Haha! In your face Mesa! Thats awesome. Just make sure you protect the newly open top of the head!

[Chef]

Really, I don't think it's a poor design.
I've had all three versions now.
Both my earlier Walkabouts I ran in the Scout, and often at 2 ohms.
I never had heat issues, even outdoors in mid-summer. The flow-thru cooling seemed very effective to me.

I no longer had a Scout cab when I got my '09 black-faced head; but I've run the new one much more often at 2 ohms than at 4 ohms. It's never flinched.

Nothin wrong with being cautious though.

[MuthaFunk]

Originally Posted by Chef

Really, I don't think it's a poor design.
I've had all three versions now.
Both my earlier Walkabouts I ran in the Scout, and often at 2 ohms.
I never had heat issues, even outdoors in mid-summer. The flow-thru cooling seemed very effective to me.

I no longer had a Scout cab when I got my '09 black-faced head; but I've run the new one much more often at 2 ohms than at 4 ohms. It's never flinched.

Nothin wrong with being cautious though.

Good to know Chef. I appreciate your first hand experience.

[BillyB_from_LZ]

Originally Posted by P. Bass

...Since a 4ohm speaker coil runs hotter than a 8ohm @ the same volume...

Please explain why this is the case...