One nice thing about Mac is they don't drive their tubes hot like ARC does. The tubes in an ARC last about 2000 hours. I'm told (having not owned a Mac) that their tubes last much longer. Also, Macs don't use a screen resister as a tube protector. When the resistor blows it flames up in a spectacular fashion. Sadly I do have personal experience with this event- twice as my bias was out of whack.
