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7B92A: Difference between revisions
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The '''Tektronix 7B92A''' is a 500 MHz dual timebase plug-in for [[7000-series scopes]]. | The '''Tektronix 7B92A''' is a 500 MHz dual timebase plug-in for [[7000-series scopes]]. | ||
It was introduced 1976, replacing the [[7B92]]. | It was introduced 1976, replacing the [[7B92]]. | ||
The 7B92A was developed after it was discovered that the 7B92's sweep ramp generator had aberrations | The 7B92A was developed after it was discovered that the 7B92's sweep ramp generator had aberrations in its start-up at the fastest sweep rates. | ||
in its start-up at the fastest sweep rates. | |||
On the 7B92A, Larson served as the project engineer and worked on the trigger circuits while | On the 7B92A, [[Les Larson]] served as the project engineer and worked on the trigger circuits | ||
[[Bruce Hofer]] designed the sweep generator, delay pickoff, and output amplifier. | while [[Bruce Hofer]] designed the sweep generator, delay pickoff, and output amplifier. | ||
An "HF Sync" triggering mode is provided in which the trigger level control varies the frequency of a built-in oscillator to lock on to the input for input signals from 100 to 500 MHz, providing higher sensitivity than the direct trigger (which is specified up to 500 MHz as well). | An "HF Sync" triggering mode is provided in which the trigger level control varies the frequency of a built-in oscillator to lock on to the input for input signals from 100 to 500 MHz, providing higher sensitivity than the direct trigger (which is specified up to 500 MHz as well). | ||
As a dual time base, the 7B92A uses the top field in the [[7000 series readout system|display readout]] | As a dual time base, the 7B92A uses the top field in the [[7000 series readout system|display readout]] for the sweep speed of the main and the bottom field for the delayed time base. | ||
for the sweep speed of the main and the bottom field for the delayed time base. | |||
The delay time can only be read from the 10-turn analog dial. | The delay time can only be read from the 10-turn analog dial. | ||
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After that, the 7B92A used a [[155-0061-00]] trigger amplifier followed by a [[155-0150-00]] trigger detector. | After that, the 7B92A used a [[155-0061-00]] trigger amplifier followed by a [[155-0150-00]] trigger detector. | ||
[https://vintagetek.org/years-at-tektronix-hofer/ According to Bruce Hofer], early 7B92 models exhibited sweep anomalies especially near the start of the sweep, and after trying to fix these he convinced management that a redesign was needed. This resulted in [[Patent US 4009399A]], the [[7B92A]] update, and the [[067-0657-00]] calibration fixture. | [https://vintagetek.org/years-at-tektronix-hofer/ According to Bruce Hofer], early 7B92 models exhibited sweep anomalies especially near the start of the sweep, and after trying to fix these, he convinced management that a redesign was needed. This resulted in [[Patent US 4009399A]], the [[7B92A]] update, and the [[067-0657-00]] calibration fixture. | ||
The 7B92A uses one other custom IC, the [[155-0049-00|155-0049-xx]] sweep control circuit. | The 7B92A uses one other custom IC, the [[155-0049-00|155-0049-xx]] sweep control circuit. | ||
The internal jumper (P834/P835) for mainframe selection (7800/7900/7100 vs. slower) | The internal jumper (P834/P835) for mainframe selection (7800/7900/7100 vs. slower) | ||
increases the minimum holdoff time on the slower mainframe selection | increases the minimum holdoff time on the slower mainframe selection by adding a 214 pF capacitor, C835, to pin 8 of the sweep control IC (U820) in parallel with the other capacitors that are selected by the sweep rate switch. This increases the minimum pulse width of the holdoff signal on [[7000_Series_plug-in_interface|pin B4]] so that the sweep logic of slower mainframes can handle it properly. | ||
by adding a 214 pF capacitor, C835, to pin 8 of the sweep control IC (U820) | |||
in parallel with the other capacitors that are selected by the sweep rate switch. | |||
This increases the minimum pulse width of the holdoff signal on [[7000_Series_plug-in_interface|pin B4]] | |||
so that the sweep logic of slower mainframes can handle it properly. | |||
The effect of this jumper is only noticeable for sweep speeds of 20 μs/Div and faster, | The effect of this jumper is only noticeable for sweep speeds of 20 μs/Div and faster, | ||
since at those sweep speeds the smallest shunt capacitance is used on pin 8, and the holdoff time is minimal. | since at those sweep speeds the smallest shunt capacitance is used on pin 8, and the holdoff time is minimal. | ||