Typical B-minus I-F Wave Traps

Typical B-minus I-F Wave Traps

The I-F bypass capacitor is used in Philco AC-DC sets from 1946 on. As you see above, it is a typical wax-paper capacitor with a coil of 6 to 8 turns of wire wound on the “outside foil” end of the body. It will be connected from a point on the B-minus buss to a ground lug or a solder spot on the chassis itself. When this wax-paper cap is replaced during restoration, the coil most likely will be of little or no effect if left out. Purists will want to preserve this wave-trap capacitor look which is alright too. Be sure to use a new capacitor with the same diameter and do not change the number of turns or any other dimension of the coil.

Here is an excerpt from a 1946 Philco service bulletin showing the schematic representation of this wave-trap capacitor. It will usually be found in the schematic on the B-minus line near the Mixer section or the I-F section.