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Old 30th May 2012, 01:47 AM   #131
Loren42 is offline Loren42  United States
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Join Date: Sep 2008
Location: "Space Coast" Florida, USA
Originally Posted by dady View Post
IMHO, dear friend, I were read this post from the year 2010 and maybe a litle obsolete, I don't know if some body of the coforers dye at this time. The fact is you have a lot of energy to build an amp similar to MCint. The answer is you can if you want (Sigmund Freud) and if you say not can is because you don't want....
Words but you need facts, in the middle of them SY is a partner of this Monster Forum, counsel you that read Morgan Jones book. I see this book for years and all the time I asked to myself, what you need this book? But one big fact is I got this book and my life change for ever. When I going to anywhere i bring my valve amplifiers. Is an amazing book.
I have a friend here in Menorca, that is cooker and play electric guitar, He doesn't know any electronics science but any at all. He got a diagram of a Fender valve guitar amp, he went to the metal store, he buy a piece of stainless steel, he cut it and he has buy every parts and he made a Fender clone that sound amazing.
Anyway Mcintosh is to different animal, maybe you can make a Porshe 911 or you can repair the gearbox of a ferrari, but the most probably fact is : you need many time for that. Now after many many time, i trying to get a Mc75 old fashion ones. Maybe is a good choice for you, get one, there are for 2000 dollars in US, you can rebuild and experiment with the circuit or changing some valves. I listen one MC275 many time ago, is euphonic to my taste. Maybe so transitorized sound like. But I want one in my living room. Previously i want it in my worktable for change some guts. Probably is a obsession like the yours. Or obstination more.
Best Regards and i hope this message helps you.
Every time I read things like this I have to roll my eyes a bit. Tube sound. I guess there is a little truth to that and there are a few reasons why that has a ring of truth.

First, there is the bit about distortion of tubes versus transistors. However, that argument falls apart when you consider that normal (if not ideal) listening levels should never induce distortion in the amp, if you size the system correctly for the task.

That means the amp should never operate in a zone where it is pushed so hard as to generate audible distortion in the first place. It doesn't matter what topology you choose, it should ever have to be overdriven to get the SPL level required for the job.

So, poof! There goes the distortion myth.

So, where is the tube sound? It turns out there is actually a tube sound, but it comes from a source that you would not expect - your speakers!

Sounds crazy (no pun intended)? Not really. You can clearly get a different sound between a tube amp and a transistor amp (running below audible distortion levels) and the difference has to do with frequency response.

In an ideal world a transistor amp and a tube amp should sound exactly the same, but speakers are not an ideal load and impedance varies with frequency when inductors are introduced to the load.

The root of the problem is the way a tube amp and a transistor amp operate into a load. A transistor amp is a Voltage Drive amplifier and a tube amp is a Current Drive amplifier - well sort of, but for this discussion we will just call it so.

What that means in a nutshell is that a voltage drive amp's power will decrease as the impedance of the speaker rises. The opposite happens when a tube amp sees a higher impedance load. its power output increases.

Now, let's consider the average speaker impedance curve over its operating frequency. The type of base cabinet (sealed versus ported) has some impact, but both tend to have a higher impedance in the bass region, which decreases in the midrange, and rises slightly in the treble region.

What does that mean to the listener? Well, a transistor amp sounds a little sterile because the bass is a bit wimpy and the treble lacks that sparkle because the power drops off as the impedance goes up.

If the impedance curve has some bumps associated with the crossover it further aggravates the problem a little.

A tube amp tends to boost the bass a little as well as the treble and just shines more than the transistor amp, which seems a bit lifeless compared to the boosted tube sound.

There are other factors at work here, but I wanted to illustrate one of the important differences that makes the two amplifier types sound the way they do.

A high end sound system with a really good speaker system (where the impedance is fairly constant) should sound about the same with a tube amp versus a transistor amp. However, most speakers are not a flat line when it comes to impedance and therefore react differently when driven by a voltage drive and current drive amplifier.

Then there is the whole subjective idea of "magic", but I refuse to go down to that level of a discussion.

The bottom line is you should correctly size your amp for the job at hand and make sure your speaker impedance is as flat as possible. Then there is the whole room acoustic thing, but that is another form.
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Old 30th April 2015, 09:22 PM   #132
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Join Date: Oct 2013
I have found a transformer well adapted for making a MC60 clone from scratch. I do a moke up and take you inform.
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Old 1st May 2015, 12:12 AM   #133
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Join Date: Nov 2007
Old thread, but I might as well add that I have built a Unity-Coupled amp with the Plitron transformers and they worked quite well. The winding resistances were quite low as well so I ended up with a very low Zout (~1 Ohm) despite the fact that I used no global negative feedback loop. It is a very nice transformer.

The main problem with the Plitron transformers is that the impedance ratio is not optimal. The transformers are rated for 70W but you have to use really high B+ to get that power output with an 8 Ohm speaker. Driving a 4 Ohm speaker would be the way to go if you wanted full power from the transformers, but I don't have 4 Ohm speakers.

If you design an amp for 8 Ohm speakers and 450-500V B+, the load line will cross well under the knee of the pentode curves because of the turns ratio of the transformer and the high screen voltage if you connect screens as McIntosh did. That bothered me, so I included a floating screen regulator to drop the screen voltage down a bit (and bring the Vg = 0 knee down as well). After loading the tubes like that, the amp delivers ~40W into 8 Ohms when driving the tubes to saturation with a B+ of 450V. To get more power than that you would have to raise B+ or go with 4 Ohm speakers. It would have been nice if van der Veen had designed these transformers with a 4-8-16 tapped secondary. Unfortunately, he didn't.

Anyway, description of my amp is here for any who are interested.
My Blog:
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Old 1st May 2015, 01:14 AM   #134
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Join Date: May 2005
Location: California
I have 2 X MC60 power transformers and 2 X MC60 output transformers. A couple of them need a paint job. If anyone is interested, make me an offer, and if I like it, they're yours. Maybe I should have posted this in the Swap Meet section...
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