To eliminate hum with receivers prior to Run No. 3, the connections from the second bass amplifier 6J5G tube to the cable socket contacts Nos. 11 and 18 (Service Bulletin No. 267), in the power unit are reversed. The grid of the 6J5G tube was wired to the shield and the shielded wire to ground. Therefore, make sure the shielded wire is connected to the grid and the shield is grounded.
From the Philco Serviceman – June, 1937.