7A11: Difference between revisions

The 7A11 was admittedly clumsy to use because of the probe size.  It had some trouble dc drift with rf pickup at 5mV, 100mV and 2V/div.  It was not very popular partially because it was expensive,  $850 for single channel vs dual channel 7A12 (105MHz) at $700.  But there was never another 1 megohm 7000 series plugin as fast as the 7A11...and it was one of the originals!   

The 7A16 (single channel plugin) was also 150MHz, but that was a year later.  Then the 7904 came out in late 1971.  That made the 7A11 a 250MHz plugin (for $950).  The 7A16 was then 225MHz (for $625).  The 7A16 disappeared rapidly and became the 7A16A, still 225MHz in 1973.  

In 1972, the 485 came out with a 250MHz 1 megohm input.  The 485 used a faster IC process ("SH2", 3.5GHz) but the 1 megohm to 50 ohm converter used only discrete devices.  (See Electronics June, 1972)

By 1974, the 7A11 cost $950 and the new, popular 7A26 (dual trace) was $1,050, not counting probes.  But that would still only get you to 50mV/div with a (9.5pF, 3 foot, X10) probe, five years after the 7A11 introduction.  Tom Rousseau designed the 7A26 which used the faster IC process and a vertical IC I designed for the 485.  The 7A26 sold so well that Tektronix presented Tom with an entirely gold plated 7A26!  Obviously, he still has it.

But using that scheme, if the 7A11 went to 20V/div,  it would have to stack three X10 attenuators inside the probe,  making it a behemouth, and even if you did, that would still leave the X2 and X5 attenuations up to gain switching in the amplifier.