I didn't carry them by the duct tape. That was so they wouldn't slide around as much in my hands, in the car, or be bumped apart as easily.

Huh? How did you put the 2x4s on there? Did it take longer for them to overheat/fail?

By feeling the bottom of the top one you noticed what I was saying earlier. The top one has more heat to get rid of.

I simply laid a 2x4 on top of the bottom amp down each side to give an additional spacing of 1.5" between the units (the top amps feet rested on the 2x4s). It did not appear to take much longer for them to shut down, however, keep in mind the amps weren't starting cool for any of the test after the first one. The were cool enough to give me a green light but still warm from the previous tests.

This was AFTER you swapped them, correct? The top amp must dissipate it's own heat as well as the heated air it is drawing in from the amp below. It sounds as if you need to isolate their air intake to get cool air to both units.

What's the surrounding area look like for these amps? From what I understand, the 200's are not prone to getting all that hot, so seeing first one and then both exhibit significant heat build-up makes me suspect that they are being starved for cool air somehow or being forced to reject heat into an already warm airstream. Are they in an enclosed space or adjacent to other heat sources?

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gonk -- 950 Review | LFM-1 Review | Pre/Pro Comparison Chart | Saloon Links

Gonk:
Yes, this is the direction I am leaning as well. The amps are in a rack in a closet. I have done a little more trouble shooting as suggested by Steve, the only test I have left is to move them out of the closet and see if it persist. My guess is that they will not shutdown when placed outside the closet. I will not be able to do this today, but I will try it this weekend.

Thanks to all for their responses.

Ed

It sounds like you've pinned down your problem; I would be surprised to see them shut down if they are outside the closet (or even if the closet door is left open, depending on the layout of the closet). A rack in an enclosed closet has a strong likelihood of heating up to an excessive degree. There are some ways to add ventilation to alleviate the problem: high and low door grilles in the door, a louvered door, or an undercut door and a ventilation "stack" or fan discharging into the attic would all allow the equipment to receive proper ventilation.

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gonk -- 950 Review | LFM-1 Review | Pre/Pro Comparison Chart | Saloon Links

I'm thinking that Gonk is on the right track here. Does you entire closet have a ventilation problem or is it just your component rack? If you have two M200s stacked in a closed-sided equipment rack inside a closet, that could easily present a problem. If the closet itself is OK, you might try a rack-mounted silent fan, activated either thermostatically or whenever you switch on your preamp (using the AC output in the back). Some of these are a bit pricey given the ridiculous markup always applied to high-end audio gear, military equipment, and women's footwear.

If you are a DIY type, you could go to Radio Scrap or CompUsa and get some "silent" computer cooling fans and rig those up to the sides of your amps. I don't normally like fan noise in my listening room, but if you have your components in a closet, that shouldn't be a problem.

I doubt that you have an electrical problem with both M200s. Mine has always stayed cool, even with a Jolida tube amplifier stacked on top and running through multiple movies at high volumes. It is mounted on top of my equipement rack, but open to the air around the sides. When driving my 4-Ohm, power hungry Magnepan CC1, you can definitely tell the M200 is throwing off some heat, but there is enough venting to dissipate it effectively. It makes sense that the top amplifier would overheat more, since the bottom one would be convecting heat right into the ventilation grille on the bottom of the upper amp. If there is poor airfloor around the sides of your components, there would be no place for the hot air to go other than roasting the upper amp. If your component rack has closed sides close to the edges of your components, you might be able to take care of your problem by cutting a slit in it where the gap between your M200s is located. If you set up a fan system, I would recommend directing the airflow between the two amplifiers, which should help keep the bottom amp from cooking the top one.

Of course, you could always go to the nearest beer distributor and get a 50-lb block of ice to set on top of your amps whenever you plan on a heavy listening session... Let me know how that one works out for you!