This is the method described in Step 8 of the MC2125 Service Manual Notes. In the end, what is the difference in results between your method and Mcintosh's?
First off , please take no offense from what i am going to say in the thread post, thank you.
The ancient Mac/kill-watt laymen method is just all of that. Its blind and un-enlighting about what else is going on INSIDE the amp. Plus I don't know of any amp maker using such an ancient way of seeing if a amp is idling correctly. Yes I measure AC power draw and DC power draw on amps as a baseline "DUH it's turning on test"
But AC or DC power draw figures vary just as much as AC line voltages and DC feed voltages do to any amp made by any maker so its at best a vague and arbitrary measurement that does not really look deep enough to see if everything inside the amp is balanced and operating properly at all...
I been doing this too long to base all my workmanship on a simple power draw test. Its a lot more involved inside of any amp then some simple idle power draw test can tell about.
Don't take this as bad mouthing Mac and their conception of everyone else's limited abilities < the only reason I know of they would tell you to test such a way for >
But McIntosh did not Invent amplifier technology, They just build and sell it. Just because they profess a laymen's way of basic testing in a service manual meant for some handyman's repair desk, it does not in any way really get you inside of any amp made to see if its really working balanced and aligned properly.
Plus I think they use that weird way of testing to check see if the amp is passing huge DC offset into those beautiful auto-transformers which HIDE errant DC offset voltages and odd behavior any amp is capable of...You see if the amp is passing DC there is no way it will be anywhere near their base current draw expectations.
I prefer to test with the transformer out of circuit to get my numbers and to test each and every emitter voltage drop for even and balanced current sharing of the output stages etc, etc, etc....BUT this requires that you have some rudimentary engineering understanding of the design in the first place. So what I do is not for the faint of heart or the untrained and uneducated. I drive deeply inside of the circuitry to make sure its all intact and functioning as expected.
There are lot of want-a-be type tech's and mechanics out there. Hell I have seen hack doctors in my lifetime. So please allow me my grace to grail chase what I know and understand to be the best repair methods I found in 35 years of doing this sort of work on the side while I engineered my way thru Silicon valley for 30 years of that. And in Silicon Valley WE made all the Silicon parts your listening to now, so I like to think I worked with some of the best in my lifetime and they taught me well along the way... So I do things infinity deeper then most Service manuals talk about.... And remember service manuals were intended for 9th graders in most cases. I know this because I have written a few in my lifetime and I was told to condense to 9th grade level language and technology limitations... I worked for GM, 3M, Kodak, Verbatim, Intel, AMD, National Semi, and some nice folks that do Military that I can not speak of, and everywhere I went I have had to condense everything to levels way below the average 2 year college level minimum requirements to be called a "Tech".... So why would you expect McIntosh to be doing otherwise in their service manuals?
I hope I have not offended you in any way but I had to elaborate in depth for you to see my point of view concerning service manuals in general and McIntosh's very vague and unrealistic testing methodology they infer in their service manuals.
I also can share Alpine, Kenwood, Adcom, Sony, SoundStream, Phoenix Gold, etc service manuals and none of them test in such a manner, and I do mean NONE of them... They require Voltage drop measurement inside of the amps circuitry to validate the amps proper operating condition, I even have some brand names rebuild line tech data and requirements, and they even require the same in-depth technical measurements to verify a amps proper internal operations.....
I have AC and DC power measurement equipment on my bench at my home even. I use it to do efficiency measurements mostly < I.E. power in versus power out testing methods for amplifier efficiency ratings etc.... But I never harness my buggy to this measurement as the sole test for any amps proper operations and anyone that does is either untrained or unknowing and therefore unqualified to be servicing amps IMHO.... The test just isn't good enough in the real world I live in and understand ...
Sorry, I am not trying to be mean, just knowledgeable in a true engineering sense. I don't open up gear that I don't completely understand how to work on and what I am looking at. It would be Un-professional from my background.
Plus I don't like looking stupid when I do what I do for anyone and I have had the honest pleasure of working for people that looked down on that sort of workmanship from their PHD level of education... So its keep up or give up,,, but don't get in the way where I came from... and I have seen a many fall to the wayside in my time... Working for well educated people beyond masters level is not the easy way of making a living...But I feel smarter for having done so in my lifetime. If it has made me hard well you should see some of the mess's I have had to clean up from want-a be's out there....That made me feel more like a janitor, then the engineer I was all my life....sad but true...
So no hard feelings I hope, I just plain Know better then what any Mac service manual preaches... plain and simple... They <Mac> build audio gear they did not invent the technology of silicon, They just use it to make money and Wow do they make a lot of money with Silicon...I actually know what building a amp costs, even a Mac amp, and Mac got huge margins in what they build and sell, why do you think three other companies have bought and owned them... They aren't going broke anytime soon... heck didn't one of the founders retire and buy a whole mountain in Arizona. Like DUH ! You don't do that losing money in business...
PS I also have a FCC license and I can work on RF amplifiers and generators for broadcast stations also. I can't begin to tell you how many DC power supplies and RF generators I repaired and rebuilt in my lifetime here and aboard in Japan used to manufacture silicon and electronics related products mind you..... It's been a long road and I am not about to change what I do now, since it has worked so well in my lifetime...:thmbsp:
It's all about the little details, and it always has been about the fine details...or none of this stuff would work at all...There is a mathematical reason for everything inside of any amp made... Its all about the numbers...or you can't design a amp from the ground up. Simple as that... again I hope no one is offended.