Grippall Dual‑range Coil

• alternative name: JR

The Grippall is a combined tuning coil and wave‑trap unit intended for broadcast receivers requiring improved selectivity in areas affected by strong local transmitters. It carries separate long‑wave and medium‑wave windings on an octagonal former, together with a dedicated trap winding permanently in circuit.

A push‑pull switch on the top plate selects the long‑ or medium‑wave coil. The assembly is supplied as a panel‑mounting unit requiring only a single fixing hole, and each coil was sold with a wiring diagram.

Waveband coverage (as reported)

• Medium‑wave tuning: approx. 225–575 metres (≈ 520–1,330 kHz)
• Long‑wave tuning: approx. 540–2,500 metres (≈ 120–556 kHz)
• Trap function: intended to suppress strong local stations; tests reported effective rejection of the Brookmans Park transmitters

Associated components (recommended in article)

• 0.0005‑µF variable condenser for tuning
• 0.0003‑µF fixed condenser for optimum trap performance

Construction

• Octagonal former carrying three windings: MW, LW, and trap
• Metal top plate with terminals and band‑change switch
• Cylindrical multi‑section coil body as illustrated in the period photograph

Purpose and performance
The unit was marketed as a practical means of reducing unwanted breakthrough from powerful regional transmitters. Tests published in Amateur Wireless reported that the trap winding eliminated interference from Brookmans Park while maintaining normal tuning ranges on both bands.

Price 1930: 10/6

In questo link sono elencati 11 modelli, di cui 10 con immagini e 0 con schemi.
Elenco delle radio e altri apparecchi della J.R. (Brand) Jean Rigaut, Grippall Electrical Products, Ltd.; London