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Re: Power Calculations - No Clipping

Posted by Legendre (A) on September 18, 2006 at 16:37:34

In Reply to: Power Calculations - No Clipping posted by Satelliteman on September 17, 2006 at 15:06:26:

Stu,

First, you need to be sure that neither the signal generator nor the oscilloscope are tied to ground. These are true balanced amps, and if any of the input or output terminals are tied to ground, it will skew the measurements (early clipping).

Ideally, both the sig gen and the scope should have floating, balanced outputs and inputs, respectively.

Also, the test should be done with new tubes, and the amps should be allowed to warm up *fully* - at least one hour of playing music, with three hours being ideal. Full hot bias for an M-60 is around 525-550mA, after 3 hours of warmup - allthough the newer models have much less upward creep of bias current than the older ones.

As a point of interest, you should find that the M-60 makes the most power into 12ohms - I was able to measure over 70W RMS into a 12ohm resistor, many years ago.

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