On some of my SE/30s depending on the fan I have super-tuned the electron beam focus/stability by adding mu-metal shielding wrapped around the glass neck exposed from the yoke collar back to the crt socket. Several turns of soft steel tin can material might be a substitute, secured with suitable tape used sparingly as not to heat insulate the neck. It's a secret! [Nice job! I like the high-res.Now if I can just duplicate it on my SE-turned-SE30...
73s 8)
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