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7A12: Difference between revisions
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[[John Addis]] writes: There were two mistakes, concept errors, that doomed the 7A12 from day one. The first was in deciding to use the 1 GHz F<sub>T</sub> Tektronix IC process (called 50/450 for resistivities of the two base layers) for the signal path. This process was Tektronix' fastest but too slow for a plugin expected to provide 150 MHz bandwidth in the fastest original mainframe, the [[7704]]. At the time, HP had a 2.5 GHz process. | [[John Addis]] writes: There were two mistakes, concept errors, that doomed the 7A12 from day one. The first was in deciding to use the 1 GHz F<sub>T</sub> Tektronix IC process (called 50/450 for resistivities of the two base layers) for the signal path. This process was Tektronix' fastest but too slow for a plugin expected to provide 150 MHz bandwidth in the fastest original mainframe, the [[7704]]. At the time, HP had a 2.5 GHz process. | ||
The second day one mistake, later pointed out by [[Tom Rousseau]], was to arrange the two channels side by side. 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 functionally attractive. However, that would require both channels to occupy the same space on a single vertical circuit board. | The second day one mistake, later pointed out by [[Tom Rousseau]], was to arrange the two channels side by side. 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 functionally attractive. However, that would require both channels to occupy the same space if on a single centered vertical circuit board. | ||
The solution was two separate, mirror image attenuators and two identical amplifier boards all attached to a main vertically-centered circuit board. Having two mirror image attenuators was obviously very expensive. | The solution was two separate, mirror image attenuators and two identical amplifier boards all attached to a main vertically-centered circuit board. Having two mirror image attenuators was obviously very expensive. | ||
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The two identical amplifier circuit boards, one mounted on each side of the center board, are cleverly flipped so both face outward from the center board. This is accomplished by having one near the top rail and the other near the bottom rail. | The two identical amplifier circuit boards, one mounted on each side of the center board, are cleverly flipped so both face outward from the center board. This is accomplished by having one near the top rail and the other near the bottom rail. | ||
Tom Rousseau designed a new dual trace plugin with discrete components on a single circuit board. One channel was above the other. This was all done on a single circuit board, had only 80 MHz bandwidth but was much less expensive to manufacture. He did this on his own, not at management's request. Management liked it and it became the [[7A18]]. Later Tom had the advantage of a 3 GHz IC process (SHF2). He used the [[M84]] (155-0078-xx), already in production for the [[485]] | Tom Rousseau designed a new dual trace plugin with discrete components on a single circuit board. One channel was above the other. This was all done on a single circuit board, had only 80 MHz bandwidth but was much less expensive to manufacture. The design was classical had none of the complicated offset circuitry, and the channel switch was the same venerable 155-0022 used in the 7A12. He did this on his own, not at management's request. Management liked it and it became the [[7A18]]. Later Tom had the advantage of a 3 GHz IC process (SHF2). He used the [[M84]] (155-0078-xx), already in production for the [[485]]. This was the 200 MHz [[7A26]]. It became the best selling Tektronix plugin of all time. Tektronix literally gold plated a 7A26 and gave it to Tom in recognition. | ||
See https://vintagetek.org/100000-7a26-plug-in/ | See https://vintagetek.org/100000-7a26-plug-in/ | ||