Grippall Tuning and Rejector Unit

• alternative name: JR

The Grippall Tuning and Rejector Unit is a combined tuning coil and interference‑rejector assembly intended for broadcast receivers operating on the long‑ and medium‑wave bands. It incorporates four separate windings on an 8‑ribbed ebonite former, together with a wave‑change switch and terminal panel mounted on a 2½‑inch square ebonite block.

The long‑wave and medium‑wave coils are connected in series, with the wave‑change switch short‑circuiting the long‑wave coil when pushed in, thereby selecting the medium‑wave range. A separate rejector winding is permanently included to suppress breakthrough from strong local transmitters.

Waveband coverage (as reported)

• Medium‑wave tuning: approx. 231–570 metres
• Upper long‑wave / lower medium‑wave tuning: approx. 950–2,050 metres
• Long‑wave tuning: approx. 850–1,080 metres (Exact ranges dependent on associated condenser values.)

Associated components (as recommended)
The article reports tests using:

• 0.0003 mfd
• 0.0002 mfd
• 0.0005 mfd
• 0.0006 mfd variable and fixed condensers to obtain the tuning ranges listed.

Construction

• Former: 8‑ribbed ebonite, 2½″ diameter × 2½″ long
• Panel block: ebonite, 2½″ square
• Windings: four coils (LW, MW, rejector, and coupling) wound by the sectional method
• Switch: push‑pull wave‑change switch
• Terminals: mounted on the ebonite block with clear access for wiring

Purpose and performance
The unit was designed to provide improved selectivity and rejection of strong local stations, functioning as both a tuning coil and a built‑in wave‑trap. Tests published in Amateur Wireless reported stable tuning across the stated ranges and effective suppression of unwanted signals.

Price 1930: 10/6

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