The Tektronix 547 Oscilloscope - Magic in the Box

Of all the big box Tektronix oscilloscopes, the 547 was perhaps the most popular. It was a single beam oscilloscope costing $1875 in 1968, the year a Ford Fairlane could be purchased for just $500 more. Tektronix had a catalog bursting with big plugin oscilloscopes. There were even four dual-beam scopes in the lineup, so what made the 547 so popular. Thre little letters on the fron tpanel: "A", "L", and "T."

Consider that it has been said the an oscilloscope is a miraculous device that lets us see electricity. Not so much electricity, as the way electrical signals are changing. Consider also that it was of interest to many users to be able to see more than one electrivcal signal on the screen at the same time, so they could be easily compared.  There were two methods of doing this. One was a dual-beam oscilloscope. In a variety of ways, one oscilloscope was really two, the two scopes coming together inside the crt, where two electron beams were directed independantly onto a single phosphor screen. You can imagine that this would be a very expensive approach, as two of everything were required. Tektronix oscilloscope like this were the 502, 551, 555, and 556. SOme of these had two timebases and two sets of horizontal deflection plates, so the horizontal scan of the two beams could be synchronized (triggered) seperatley from the other.

Another way to do the same thing was to use an electronic switch in front of the vertical system in a single beam oscilloscope. This is called a "dual trace" oscilloscope. The switch worked to display 2 or 4 seperate electrical signals on the screen. This required little duplication and added only a small amount to the cost. This is the technique used in all the dual and four-trace plugins such as the CA, 1A1, 1A2, Type M and 1A4.

But where did this leave us horizontally, so to speak. While there was a composite signal from the input signals being sent to the vertical deflection plates, the horizontal system still only had one set of deflection plates, driven by one sweep from the  sweep generator in the timebase. This meant that even in oscilloscopes with an "A" and a "B" sweep, only one of them could drive the crt at a time.

So why couldn't they just use an electronic switch in the horizontal system too, and switch between the two sweep generators in harmony with the two input signals. It is an oversimplification, but that is exactly what the engineers at Tektronix did, they developed alternating horizontal sweeps for the 547. That is the magic in the 547 box. It was a huge job, and required diode switching to display the correct sweep to match the input signal. For the first time, a single beam oscilloscope could display two or more electrical signals that weren't related in time, with independent sweep speeds for each..

Of course, this wasn't the only thing that made the 547 such a hit. How about DC to 50 mHz bandwidth? And tunnel diode triggering to over 50 mHz, in BOTH sweeps. Not even the 585 had such sophisticated triggering in the "B" sweep. There was the new crt with an internal graticule. And of course it accepted all of those plugins that Tektronix was famous for.

While at the ARRL Hamfest at Seaside Oregon in 2006, I was fortunate to be able to acquire a very nice piece of 547 history. I was able to purchase Serial Number A06, a pre-production 547! Not only was it pre-production, it was the very 547 that was used to introduce the new model at the March, 1964 IEEE Convention in New York. Jack Murdock and Howar Vollum are shown in a picture with this actual scope on page 258 of the "40 Years" book. Bob Rullman, one of the Tektronix engineers and a designer of the 547, told me that they set up this scope in the hotel room and then took each journalist in, one at a time, to study the new model. Bob has been kind enough to send me the original manual and the original copy of the press release, produced on something called a typewriter. Some of you may remember what that is! LOL