Understanding Mcintosh Meters?

Precisely.The 7270 has the big beauties that are window dressing.YMMV,Bob

"Blue Meter" with glass front, nice looking, but totally worthless!! Don't worry about the meters they will never tell a story on your speaker or systems capability, if it sounds good go with it, you will know just like everybody else having amps with NO meters when there is an issue of being overdriven. I owned several mcintosh pieces over the years, basically you can buy white ipod or you can buy a fancy "Skined" Ipod to make it look better, thats all the meters do for you, they give you a unique look.

Totally worthless? Don't know about that. Does a car need a tachometer? No, but I like knowing what's going on engine wise. Same with audio. They will let you know when you're about to "redline" the amp (not the speakers though).

To the OP: Don't know the 6450 that well, but I think it's new enough that it should have a "power guard" or "power sentry" monioring circuit that would take the guess work out of meter calculations.

Above all else, your ears are the best meters. Turn up the volume slowly until you begin to hear stress out of the speakers, note where the meters are and keep it under that level. It doesn't take long to burn out a tweeter or part of a crossover it you go into clipping too long.

Thanks for all the responses.

Ok, Now I am little more confused. I thought there was greater danger having an underpowered vs a overpowered amp because the underpowered amp could clip, causing distortion, and that is what damages speakers.

Musicnoise: You said that as long as I am supplying less wattage than my speakers can handle I am fine. So does that mean if my amp is say 50-100 wpc (depending on speaker impedance) and my speakers are rated at 350w power handling, I dont have to worry about frying them with my amp? But then why does everyone say an underpowered amp is more dangerous?

Onemug: Yes, my amp does have powerguard. This means that my speakers should be protected against any spike in the music that may cause the amp to clip? I have already put my volume much louder than I could ever use it in my current living sitation and the powerguard lights did not illuminate, so I am just asking more for peace of mind and understanding.

Thanks for all the help guys.

Musicnoise is correct in the sense that McIntosh's Power Guard circuit will essentially keep the amp from clipping to any significant degree . . . and amplifier clipping causes the overwhelming majority of (power-related) speaker failures. And I agree with others that a simple wattmeter of any sort is of very limited use for preventing speaker damage . . . your ears and basic common sense are better things to go by.

But for your specific meter accuracy question, it varies from model to model. For the amps without autoformers (including IIRC the 6450), it's essentially a voltmeter, calibrated to a specific impedance load. So when your meter reads "100 watts", what it really means is "20 volts" . . . which is the same thing IF the amp is driving a 4 ohm resistive load . . . which your loudspeaker is obviously not. But in your case, "100 watts" on the meter will still be pretty close to the maximum power output when driving your speakers, so concept of "meter full scale" is the same, but the wattage calibration will be inaccurate.

For the later McIntosh amps that have autoformers, the meters are much more accurate, because it's the drive to the autoformer that's measured, not the voltage at the speaker terminals. They also have a current sensor that gives a certain amount of correction factor for the typical variations in a loudspeaker load. So if the load on, say, the 4-ohm autoformer tap is maybe within +/- 20% of 4 ohms, the meter reading will be very accurate. But if you were to put a 2-ohm load on the 8-ohm tap, this would be outside of the correction range of the current sensor, and the meter wouldn't be accurate at all.

But in the real world, the 6450 isn't a hugely powerful amp . . . and with clipping removed from the picture by the Power Guard, you really shouldn't need to worry a whole lot with an average domestic loudspeaker. The meters are handy for checking i.e. channel balance on a mono record, or verifying that your cables are hooked up correctly, or as an educational tool to understand the rough relationships between power and SPL, but they're not sufficient to really tell when you're about to damage your speakers.