So, can I run a Hafler DH-500 without the lid?

[Bogie]

It showed up in the fedex today, and had something rattling... Turns out that someone had taken a foot off it or something, and the rattle was a washer.

So, should I put the lid back on it before I bolt it into the rack?

[markp]

Most modern amps use the case for rigidity and heatsink so it should be on the amp.

[slowhands]

I would suggest replacing the cover. There are several reasons, dust control, protection of the fragile components on the boards and chassis strength. I have several of these without covers, and wish I had the covers.

The forced air cooling on these amps degrades when the cooler gets full of dust, which it will after a few years. There are dust filters on the input ducts that help a little with this. Short term you may have better cooling because the airflow is less restricted, but long term the dust buildup is fatal. You probably should vacuum the heatsink every year in any case.

As you can see, the components on the amp boards, especially the heatsinked transistors in TO-5 cans, get bent easily in handling and break due to fatigue, which can fry the output MOSFETs, an expensive repair. The cover protects them from harm.

Finally, the chassis is flimsy without the cover. I had to put an angle bracket from front panel to base to make the structure strong enough to rack mount from the front panel alone, which some folks do. The amp is so heavy this is probably not a great idea, because the panel bends, but it may work for you if you don't move the rack much.

[djk]

"I have several of these without covers, and wish I had the covers. "

Sound Valves/Values has them on eBay.

[Enzo]

I don't know that unit, but many amps need the lid for proper cooling. In units with a fan, the lid is part of the air duct - it helps direct the airflow over the parts that need it. Without the lid, air blows everywhere, but with the lid air blows across the hot parts.

In convection cooled units, again the lid directs the air flow. it either determines where hot air exits or where cool air enters, but either way it sets up a path to create a good convection current of air. Without a lid, hot air rises out of hte unit, but it may not then flow past all the parts doing so.

I work in pro audio, so we have many racked amps, and I can think of several models that will thermal if operated without the covers for more than a few minutes.

In racks this is especially important since the space over and under cannot be relied upon adn front to back venting is common. Make sure the back of the rack is open so it can breathe.