If you follow electronics history, few names were as ubiquitous as RCA, the Radio Corporation of America. Yet in modern times, the company is virtually forgotten for making large computers. [Computer History Archive Project] has a rare film from the 1970s (embedded below) explaining how RCA planned to become the number two supplier of business computers, presumably behind behemoth IBM. They had produced other large computers in the 1950s and 1960s, like the BIZMAC, the RCA 510, and the Spectra. But these new machines were their bid to eat away at IBM’s dominance in the field.

RCA had innovative ideas and arguably one of the first demand paging, virtual memory operating systems for mainframes. You can hope they were better at designing computers than they were at making commercials.

In 1964, [David Sarnoff] famously said: “The computer will become the hub of a vast network of remote data stations and information banks feeding into the machine at a transmission rate of a billion or more bits of information a second … Eventually, a global communications network handling voice, data and facsimile will instantly link man to machine — or machine to machine — by land, air, underwater, and space circuits. [The computer] will affect man’s ways of thinking, his means of education, his relationship to his physical and social environment, and it will alter his ways of living. … [Before the end of this century, these forces] will coalesce into what unquestionably will become the greatest adventure of the human mind.”

He was, of course, right. Just a little early.

The machines were somewhat compatible with IBM computers, touted virtual memory, and had flexible options, including a lease that let you own your hardware in six years. They mention, by the way, IBM customers who were paying up to $60,000 / month to IBM. They mentioned that an IBM 360/30 with 65K was about $13,200 / month. You could upgrade with a 360/30 for an extra $3,000 / month, which would double your memory but not double your computing power. (If you watch around the 18-minute mark, you’ll find the computing power was extremely slow by today’s standards.)

RCA, of course, had a better deal. The RCA 2 had double the memory and reportedly triple the performance for only $2,000 extra per month. We don’t know what the basis for that performance number was. For $3,500 a month extra, you could have an RCA 3 with the miracle of virtual memory, providing an apparent 2 megabytes per running job.

There are more comparisons, and keep in mind, these are 1970 dollars. In 1970, a computer programmer probably made $10,000 to $20,000 a year while working on a computer that cost $158,000 in lease payments (not to count electricity and consumables). How much cloud computing could you buy in a year for $158,000 today? Want to buy one? They started at $700,000 up to over $1.6 million.

By their release, the systems were named after their Spectra 70 cousins. So, officially, they were Spectra 70/2, 70/3, 70/5, and 70/6.

Despite all the forward-looking statements, RCA had less than 10% market share and faced increasing costs to stay competitive. They decided to sell the computer business to Sperry. Sperry rebranded several RCA computers and continued to sell and support them, at least for a while.

Now, RCA is a barely remembered blip on the computer landscape. You are more likely to find someone who remembers the RCA 1800 family of CPUs than an actual RCA mainframe. Maybe they should have throw in the cat with the deal.

Want to see the IBM machines these competed with? Here you go. We doubt there were any RCA computers in this data center, but they’d have been right at home.

One of the good things about simulating circuits is that you can easily change component values trivially. In the real world, you might use a potentiometer or a pot to provide an adjustable value. However, as [Ralph] discovered, there’s no pot component in LTSpice. At first, he cobbled up a fake pot with two resistors, one representing the top terminal to the wiper, and the other one representing the wiper to the bottom terminal. Check it out in the video below.

At first, [Ralph] just set values for the two halves manually, making sure not to set either resistor to zero so as not to merge the nets. However, as you might guess, you can make the values parameters and then step them. 

By using .step you can alter one of the resistor values. Then you can use a formula to compute the other resistor since the sum of the two resistors has to add up to the pot’s total value. That is, a 10K pot will have the two resistors always add up to 10K.

Of course, you could do this without the .step and simply change one value to automatically compute both resistors if you prefer.

We’ve done our own tutorials with .step and parameters if you want a little more context. You can even use this idea to make your own custom pot component.