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that is on a separate small board. The input amplifier contains a JFET source-follower buffer | that is on a separate small board. The input amplifier contains a JFET source-follower buffer | ||
that uses a [[2N5911|2N5911A]] (Tektronix part number 151-1032-00) biased with a drain current of 12.5 mA | that uses a [[2N5911|2N5911A]] (Tektronix part number 151-1032-00) biased with a drain current of 12.5 mA | ||
and | and V<sub>gs</sub> of –0.26 V. The input amplifier has unity gain, high input impedance, and an output impedance of | ||
about 120 Ω. The input amplifier drives a Tek-made differential amplifier chip, part number [[155-0050-01]]. | about 120 Ω. The input amplifier drives a Tek-made differential amplifier chip, part number [[155-0050-01]]. | ||
The original instrument design utilized an all-discrete switching power supply, making this an incredibly light portable scope. | The original instrument design utilized an all-discrete switching power supply, making this an incredibly light portable scope. | ||
Unfortunately, this power supply was extremely difficult to troubleshoot when it went belly-up. | Unfortunately, this power supply was extremely difficult to troubleshoot when it went belly-up. | ||
At serial number B500000 and later, the design of the supply was simplified | At serial number B500000 and later, the design of the supply was simplified to use the same basic circuitry as found in the [[7704A]] using a [[155-0067-02|Tek-manufactured controller chip]]. | ||
to use the same basic circuitry as found in the [[7704A]] using a Tek-manufactured controller chip. | |||
==Repair Issues== | ==Repair Issues== |