By Jack Ganssle

The Modern Oscilloscope

Published 4/30/2007

Sixty years ago Tektronix introduced their first product, the model 511 oscilloscope. Not just a knock-off of some standard scope design like the ones complacent Dumont were marketing, the 511 was the first scope with triggered sweep. This product launched both Tek and the modern scope.

We take triggering for granted today, but not so long ago inexpensive scopes didn't have it. In the 60s my dad took a home-ed electronics class from Devry in which he assembled a combination scope/VTVM (Vacuum Tube VoltMeter - the "Fluke" of the era), which he passed on to me while I was in 8th grade. Untriggered, it simply kept sweeping the beam, synchronized to nothing. As I recall a "sync" knob varied the time base to stabilize - somewhat - the display, but that meant it was tough or impossible to measure time with much accuracy.

Howard Vollum designed Tektronix's first scope in 1946 but it was impractically large, being spread out over an entire workbench. He and machinist Milt Brave redesigned the unit, releasing it as the 511 in 1947.

Though sold as a portable unit it weighed in at a backbreaking 50 pounds. It offered 10 MHz bandwidth, though "MHz" wasn't used in this country then so the data sheet specified bandwidth in "MC" or "mc" for megacycles. Fastest sweep rate was a blinding .1 usec/division.

There's a good picture of the unit here: http://www.geocities.com/r_corriveau/500/511.html#tline . The design presaged the modern oscilloscope in a way; in the 50s Tek's wildly-popular 500 series, and then later the 7000 series in the 60s, sported a modular design where the scope had one or more plug-in modules. Big holes in the instruments' chassis were filled with vertical and/or horizontal units of differing specifications. That fad died out; today, as in 1947, scopes generally don't have plug-ins.

The unit cost $795 in 1947 dollars, or about $7300 at today's rates. That seems a bargain when you consider that it was a high-performance, highly-innovative product that had little direct competition. Today the company's TDS6000 series can price out at more than $100k.

I can't find a manual for the 511, but one for its immediate successor, the 511A - with schematics! - is here: http://bama.edebris.com/manuals/tek/511aearly/ . A rough count identifies about 33 vacuum tubes, of which only two are twin triodes. 13 of those are in the power supply, so the scope's "smarts" use only about 22 active elements! In modern terms, 22 transistors. No multicore. No DSP.

Those tube engineers sure were great designers.

A decade later Tek's extremely popular 545 had a mere 102 tubes, yet offered so much performance that that series was still in use 30 years later.

The company sold $27K worth of 511's in 1947, growing by an order of magnitude the following year. Today they're a billion dollar company. There's little loyalty to companies anymore, but many old-timers still fondly recall their experiences with Tek's products. Me, I worked with the 7000 series in the 70s, instruments that were just a delight to use. Small illuminated interlocked buttons and selector switches with perfect detents were magnificently fitted to human hands. I had an ancient 545 that never failed - I never even changed a tube. But around 1990 it had been sitting neglected for a long time. No one wanted it and I junked the thing. Now it's a museum piece.

What was your experience with early scopes?