321
The Tektronix 321 is a very compact single-trace, single-timebase portable oscilloscope that is almost completely solid state. The 321 includes several germanium bipolar transistors, which are a known reliability problem. The 321 and 321A have slightly different circuits. Early instances of the 321 (sn pre-720) use a 5718 peanut tube as the front-end cathode follower. Later 321 and 321A use a 7586 nuvistor for that role. In several circuits, the 321 uses OC170 transistors where the 321A uses 2N2207 transistors.
Tektronix 321 factory calibration procedure
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front view
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right case
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left internal
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right internal
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rear view
