[Steve Davis]

Mark, is your 90 an early (PP-45 output) version or a mid (single 47 output) and which IF trimmer is it you are pushing on? Since it did not shock you, I'm guessing, it was one on the secondary side of one of the IF transformers (the ones on the primary side of the IF transformers have B+ on them.) If the trimmer is on the secondary side of the transformer and is grounded, the ground is provided by the mounting bolt. Make sure, the mount bolt is tight. I would use a clip lead from the chassis to the grounded side of the trimmer, to make sure. Sometimes these trimmers get corrosion between the hollow brass rivet and the back plate. This causes the ground to be intermittent.

Steve