Was the Electoral College really intended as a device against tyranny of the majority?

Not necessarily the tyranny of the majority. More like, to weed out undesirable political movements, such as moves toward violence.

Alexander Hamilton explains and defends the purpose of the electoral college in Federalist Papers No. 68. Basically, he says the reason for it is to ensure that people of "ability and virtue" are elected President. The Electoral College is supposed to ensure this since the electors were intended to be men "capable of analyzing the qualities adapted to the [office]" of the Presidency.

The Constitution leaves it up to the individual states on how to select their own electors, but Hamilton assumed it would have some component of the popular vote. He goes on to say:

"It was also peculiarly desirable to afford as little opportunity as possible to tumult and disorder...[T]he precautions which have been so happily concerted in the [Electoral College], promise an effectual security against this mischief...[A]n intermediate body of electors will be much less apt to convulse the community with any extraordinary or violent [political] movements."

Source.

There is one component of it that could partially be seen as a device against tyranny of the majority, and that's how they settled on the ratio of electors that each state got: it favors less-populated states. However, this was less an intentional device against tyranny, and more a result of the original states trying to compromise in order to stick together. The Constitution was written at a time, of course, when any of the states could have walked away and decide to form their own country, which everyone at the Convention wanted to avoid. So the bigger states placated the smaller states by getting a representational advantage in picking a President.

EDIT: On that last point, yeah, it did have something to do with slavery, because the Southern states were most of the less-populated states, and the slavery question was one of the biggest hangups among the Thirteen Colonies insofar as uniting as one country and not seeing any of the states walk away.

You can see some of the minutes of the Constitutional Convention here. Several different members of the Convention threw out their own plans for the ratio of electors, mostly favoring their own state's interests. In the end, each state got one elector for each member they had in the House and Senate.

So I literally just posted about this on my blog yesterday and again in another post, so I'll copy and paste part of my answer from that. If you are interested in a more detailed answer or background into what system they had before it, check out my blog where I deal with that in greater detail and more context (and more sources). In order to answer your question, background information on how the electoral college fits into the US Constitution is necessary.

The goal of the Constitutional Convention in 1787 was to create a new government in secret from the American people. They wanted to emerge from the convention with grand announcements over their new government which left them, the Founders with more power than they ever had before. The Founders desired to replace the Articles of Confederation, a much more republican style of government, with a new one that took power away from the much more democratic states. Let me be clear when the Founders designed this system, they fully were aware that a person could become president who wasn't the popular choice of "The People," but this is exactly why they created the Electoral College in the first place! But how and why did the Electoral College factor into their grand plans? After all, wasn’t the goal of the American Revolution to promote democracy? Well, the war was very much about democracy – but the previous decade really started to make the Founders want to limit democracy’s power.

The Convention

The men who showed up in Philadelphia in the summer of 1787 had a clear agenda for this new government. They wanted more power for the national government, and less for the states. They also wanted to limit democracy. Let me be clear, they didn’t want to return to a monarchy or anything of that sort, but they didn’t want the masses to have as much control over politics. The Founders believed that they, the educated and wealthy elites, understood the way the world operated better than farmers or merchants at the state level did.

We see this clearly when the whole convention started with the Governor of Virginia, Edmond Randolph saying , "Our chief danger arises from the democratic parts of our constitutions… none of the [state]… constitutions have provided sufficient checks against democracy.”[1] “Checks against democracy”? Yes, the whole convention kicks off by the leaders essentially saying, “look, this democracy thing is a good idea, but all the states are taking this too far – let’s rethink how we can fix this.”

There were some radical ideas thrown out there (Hamilton, for instance, wanted senators to be selected by state leaders and be in the position for life), but eventually they agreed on a system similar to what we have today – a two party legislature, an executive branch, and a judicial branch. But it didn’t look exactly like we have it today. First, the House of Representatives would be appointed by a popular vote in large voting districts. This sounds good at first, but the size of the districts were intentionally problematic for democracy to work. It embolden wealthy men to be the only ones who could achieve unity in large areas of the population since they had the time and money to travel around and gain support. Second, the senate would have their positions appointed by state legislatures not elected by a popular vote. And third, of course, was the office of the president, who would be appointed by delegates to an “electoral college” who were actually free to cast their ballot against the popular vote. But why did they do this? Why did our early government look so different? It’s because, just like their desire to have checks and balances in the government, they wanted checks and balances against democracy.

Consequently, leading men in each state calling themselves Federalists decided to create a new national Constitution that barred states from passing popular economic policies and to establish a new federal government that would, in the words of Alexander Hamilton, contain “the amazing violence and turbulence of the democratic spirit,” which had produced paper money, war debt revaluation, and debt relief and every other “popular” policy that had “spread like wild-fire” during the 1780s. [2]

So the creation of this Electoral College was another way that they could protect their own interests.

The Electoral College

One of the big topics of debate at the time was how to elect a president. They discussed/debated it for 21 days of the convention! [3] Some argued it should be a vote by Congress, while a few dissenters thought a popular vote would be better. Eventually they compromised, resulting in what is now Article ii, Section 1, clauses 2-4 of the US Constitution. Each state could elect or appoint “electors” who would vote on their states’ behalf. Usually it would be the state legislatures that would appoint these electors. The only real limit on who could run was that a person who was holding public office couldn’t fill this role. After they casted their ballots, they would tally up the votes and whoever had the majority of votes would win. If no one earned a majority, then the decision would go before the House of Representatives.

So what did all this mean? Why create a barrier between the will of the people and the appointment of the president? Well, I’ll let Alexander Hamilton himself tell you why. He believed that the appointment of the president should only be made “by men most capable of analyzing the qualities adapted to the station [of president].” In other words, he didn’t think that the average voter was capable of picking a qualified person for president. What’s funny is that this is one of the points Hamilton made publicly about the process. In private, many of the Founders talked about their fears of “mob rule.” Hamilton thought the people would be glad that they weren’t letting just any white dude vote for the president. For Hamilton, there was fear that “The People” might get caught up in following some demagogue, like Daniel Shays in Massachusetts, rather than a “more legitimate” leader. This provided a way for the elites to ensure that if the popular masses followed someone whom they disapproved of, the college could turn the other way. Just to be clear, the system was designed so that members of this electoral college could vote against what “The People” wanted without any real negative repercussions. There’s actually a term for one of the guys switching their vote from whom they are pledged to vote for and it’s called “faithless elector.” There’s actually been 22 instances of at least one or more electors doing this in US history.

Regardless of the few benefits to having the Electoral College, many historians of the Revolutionary Period believe that this was primarily intended as a barrier against democracy. One such historian even said when examining this topic, “writers as J. Allen Smith and Charles Bear, maintained that the complicated indirect method instituted for selecting a chief executive was a reflection of the Founding Fathers’ deep distrust of democracy. The Framers, according to that view, deliberately precluded popular choice of the president to ensure that the leveling force of the masses would not threaten the right of the [gentry].” [4] Essentially, many historians believe that there’s no real way to deny that this was a deliberate action by the Founders over their distrust over the masses.

Tl;Dr The Founders designed the system using the Electoral College because they had little faith that the Masses would consistently want the right person as president, so they created a system that could bypass democracy to instill leaders that the political elites approved of.

John R. Vile. The Constitutional Convention of 1787: A Comprehensive Encyclopedia of America’s Founding, Volume 1. pp 284
Terry Bouton. Taming Democracy: "The People," the Founders, and the Troubled Ending of the American Revolution Oxford University Press. (p. 176).
Shlomo Slonim “The Electoral College at Philadelphia: The Evolution of an Ad Hoc Congress for the Selection of a President” The Journal of American History, Vol. 73, No. 1 (Jun., 1986), pp. 35-58
John J. Turner Jr.. “One Vote for the Electoral College” The History Teacher, Vol. 40, No. 3 (May, 2007), pp. 411