Alistair Thomson
Forum Participant

Don’t you just hate that! 🙂

Radiomuseum.org has a lot on the S38, including the pdf attached, which talks about AC hum causes, and mentions both the switch and the mounting grommets. It looks like the mounting grommets need to have almost perfect insulation otherwise hum develops at high DC resistance. If there’s a total short between the case and the chassis, then what happens probably depends on where you connected the ground. Where did you make that connection?

The antenna-to-ground strap is not the problem: that strap is used when you have a long-wire type of antenna. With a balanced antenna you would remove it.