Referring to Service Bulletin No. 228, it is recommended that the flexible resistors Nos. 53, 148 and 151 be checked and replacement made of the one found to be at fault. These resistors are of the wire-wound type. Some have been found where the electrical connections at the pigtail leads had a tendency to loosen or stretch, causing noise in reception, especially when the receiver is operated at extreme bass response.
From the Philco Serviceman – June, 1937.