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The design includes an interesting DC restoration circuit, identical to the RCA 621TS and 721TS. I found that black level was reasonably well clamped by grid rectification on the final 12AU7 stage. The sync is positive going at the 12AU7 grid which will cause it to draw current, charging the 0.05uF coupling capacitor to peak sync level. This will bias the 12AU7 with the sync tip close to ground. The plate of the 12AU7 is DC coupled to the CRT grid.
When I was restoring my 721TS I was surprised how well it seemed to work. Has anyone seen reference to this clever design?
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10-26-2022, 05:58 PM
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