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549: Difference between revisions
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Like many Tek scopes from the period, it uses a mix of transistors and tubes. For example, consider the buffer amplifier in the 549, whose purpose is to interface the high-impedance output of the plug-in with the low-impedance of the 200 nanosecond delay line in the 549. | Like many Tek scopes from the period, it uses a mix of transistors and tubes. For example, consider the buffer amplifier in the 549, whose purpose is to interface the high-impedance output of the plug-in with the low-impedance of the 200 nanosecond delay line in the 549. | ||
As is usual in oscilloscope vertical circuits, the requirement is to have flat frequency response from DC to the maximum frequency of the scope and to have linear phase response over this same frequency range. In the 549, this buffer is implemented as follows: A [[6DJ8]] tube configured as a cathode follower is used at the interface with the plug-in to present a high impedance to the plug-in. This input stage drives an NPN BJT differential amplifier, which operates at the bottom of a cascode configuration with a [[7119]] tube on top. The output of the cascode (the plate of the 7119) drives the delay line. Since the entire signal path is differential, the common-mode voltage does not have to be zero, and it is not; the differential signal in the delay line rides on 167 volts of DC. After the delay line, the signal enters another cascoded differential amplifier with | As is usual in oscilloscope vertical circuits, the requirement is to have flat frequency response from DC to the maximum frequency of the scope and to have linear phase response over this same frequency range. In the 549, this buffer is implemented as follows: A [[6DJ8]] tube configured as a cathode follower is used at the interface with the plug-in to present a high impedance to the plug-in. This input stage drives an NPN BJT differential amplifier, which operates at the bottom of a cascode configuration with a [[7119]] tube on top. The output of the cascode (the plate of the 7119) drives the delay line. Since the entire signal path is differential, the common-mode voltage does not have to be zero, and it is not; the differential signal in the delay line rides on 167 volts of DC. After the delay line, the signal enters another cascoded differential amplifier with | ||
NPN BJTs on the bottom and 8608 tubes on the top. The vertical deflection plates of the CRT are driven by the plates of a | NPN BJTs on the bottom and [[8608]] tubes on the top. The vertical deflection plates of the CRT are driven by the plates of a 8608 10-watt power pentode, through inductive matching/peaking networks. The 549 is unusual among 54x-series scopes in that it does not use a distributed vertical amplifier. | ||
Triggering is done using an NPN BJT Schmitt trigger. | Triggering is done using an NPN BJT Schmitt trigger. | ||