[TA Forbes]

In my case (AK 92) it turned out to be a speaker wire making intermittant contact. At first I thought the 2K ohm coil was open, but it was the wire just above the jack. This would cause max B+ being felt at the - side of the cap that was failing.

Rewired the entire jack, as there were 2 more wires approaching the condition of the bad one, and am listening to the race on the AK as I write this.