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7A11: Difference between revisions
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In 1972, the [[485]] came out with a 250 MHz, 1 MΩ input. | In 1972, the [[485]] came out with a 250 MHz, 1 MΩ input. | ||
The 485 used a faster IC process ("[[SH2]]", 3.5 GHz) but the 1 MΩ to 50 Ω converter used only discrete devices. (See Electronics June, 1972.) | The 485 used a faster IC process ("[[SH2]]", 3.5 GHz) than was available for first generation 7K instruments but the 485's 1 MΩ to 50 Ω 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. | 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 50 mV/div with a (9.5 pF, 3 foot, × 10) probe, five years after the 7A11 introduction. | But that would still only get you to 50 mV/div with a (9.5 pF, 3 foot, × 10) probe, five years after the 7A11 introduction. | ||
[[Tom Rousseau]] designed the 7A26 which used the faster IC process and a [[155-0078-00 | vertical IC I designed for the 485]]. | [[Tom Rousseau]] designed the 7A26 which used the faster SH-2 IC process and a [[155-0078-00 | vertical IC I designed for the 485]]. | ||
The 7A26 sold so well that Tektronix presented Tom with an entirely gold plated 7A26! | The 7A26 sold so well that Tektronix presented Tom with an entirely gold plated 7A26! | ||
Obviously, he still has it. | Obviously, he still has it. | ||
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But using that scheme, if the 7A11 went to 20 V/Div, it would have to stack three ×10 attenuators inside the probe, making it a behemoth, and even if you did, that would still leave the ×2 and ×5 attenuations up to gain switching in the amplifier. | But using that scheme, if the 7A11 went to 20 V/Div, it would have to stack three ×10 attenuators inside the probe, making it a behemoth, and even if you did, that would still leave the ×2 and ×5 attenuations up to gain switching in the amplifier. | ||
Problem with gain switching is, the bandwidth and transient response tend to change when you change amplifier gain. | Problem with gain switching is, the bandwidth and transient response tend to change when you change amplifier gain. If gain switching was accomplished by changing emitter resistors, dc balance changed with every gain change. That meant that the VAR gain control and fixed gain selection required two dc balance controls. That would be unpleasant (see 7A13). | ||
The greater the gain change, the greater the bandwidth/transient response change in the amplifier. | The greater the gain change, the greater the bandwidth/transient response change in the amplifier. | ||
The more gain settings you had, the worse it got due to longer leads and more parasitics. | The more gain settings you had, the worse it got due to longer leads and more parasitics. | ||
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The JFET causes a small change in transient response, but not a bad one. | The JFET causes a small change in transient response, but not a bad one. | ||
[[Ron Peltola]] (of [[Peltola connector]] fame) designed the probe attenuator, Glenn Bateman and Ron designed the probe amplifier. I helped on the probe amplifier. | [[Ron Peltola]] (of [[Peltola connector]] fame) designed the probe attenuator, Glenn Bateman and Ron designed the probe amplifier. I helped a little on the probe amplifier. | ||
</blockquote> | </blockquote> | ||