7A12: Difference between revisions

The '''Tektronix 7A12''' is a 120 MHz dual-trace vertical plug-in for [[7000-series scopes]]. This original 7000-series plugin allows to compensate large dc offset voltages, however the offset voltage is not available on the front panel to be measured externally as with the [[7A11]].

There were two mistakes, concept errors, that doomed the 7A12 from day one.  The first was in deciding to use the Tektronix IC process (the "Standard Process") for the signal path.  This process had an Ft of only 1 GHz, too slow for a plugin expected to provide 150MHz bandwidth in the fastest mainframe, the 7704.

The second day one mistake, later pointed out by Tom Rousseau, was to arrange the two channels vertically.  Roy wanted to be able to go from one sensitivity (deflection factor) to another without having to go through all the sensitivities in between as happens with a rotary switch.  The vertical row of push buttons was attractive an functional.  The complexity required three circuit boards, two identical circuit boards, one on each side of a center board. That is expensive and complex.

Tom Rousseau designed a new dual trace plugin with discrete components that had 80 MHz bandwidth on a single circuit board and was much less expensive to manufacture. He did this on his own, not at management's request.  Management liked it. It became the 7A18.  Later Tom had the advantage of a later, faster IC process.  He used the M84 (155-0078-xx), already in production for the 485, and circuitry similar to the 7A18.  This became the 200 MHz 7A26, the best selling Tektronix plugin of all time.  Tektronix made a literally gold-plated 7A26 and gave it to him in recognition.