Re: Tektronix 465B Scope - Some problems.
Just had a look at my manual, unfortunately the HV and tube sections are missing. As a guess I would think that the focus and brightness circuits are fed from an inverter. Smoothing failure here would put ripple on the focus voltage so the spot will never reduce beyond a certain diameter. One of the other pictures shows brightness variations over the trace length. This would occur when the sweep speed is similar to the inverter frequency.
Al
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I won't tell you how I discovered that.
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