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Potentiometer: Mallory Volume Control on a Tung-Oil Paper Ring

L. E. Lawrence and R. O. Lewis · Public domain (expired patent)

创建者

21. 十月 2026

Potentiometer: Mallory Volume Control on a Tung-Oil Paper Ring

A 1930s radio volume control from Mallory's patent (US 2,144,925, 1939). A carbon ring sits on a base of two resin-fibre discs. A spring arm on the shaft wipes the ring with one contact and a centre metal ring with its fingers, so turning the knob changes the resistance between the centre lug and either end lug. The patent gives no sizes; the parts are named by what they do. The picture: the patent's drawing (Figs. 1 and 2).

中级

2 hours

说明

Clamp the two base discs on the bushing

Stack two discs of resin-impregnated fibre. A metal bushing through their centres clamps them together, with a metal disc clamped against the back of the rear disc. Ours: close the bushing with a hammer and rivet set.

此步骤所需材料：

树脂浸渍纤维盘2 个

金属衬套1 个

金属背盘1 个

所需工具：

铆钉锤

铆钉工具组

Fit the centre contact ring

Lay the metal contact ring, with its own terminal lug, on the face of the front disc, centred. An eyelet (or rivet) through the lug holds it. Ours: set with a rivet set and hammer.

此步骤所需材料：

带接线片的接触环1 个

空心铆钉1 个

所需工具：

铆钉锤

铆钉工具组

Bolt on the resistance ring

Lay the carbon resistance ring on the front disc, round the contact ring. Two terminal bolts pass through the ring's silver-painted ends and the disc; each holds a terminal lug under the disc. The bolts clamp the ring and connect its ends.

此步骤所需材料：

碳电阻元件1 个

接线螺栓2 个

接线片2 个

所需工具：

尖嘴钳

Fit shaft and spring contact arm

Put the shaft through the bushing. On its front end fix the spring contact arm over a small piece of sheet insulation: upset the shaft end to hold the insulation, and clamp arm and insulation together with a rivet pin. The arm's contactor rides on the carbon track, its fingers on the contact ring.

此步骤所需材料：

控制轴1 个

弹簧触点臂1 个

绝缘片1 个

铆钉销1 个

所需工具：

铆钉锤

铆钉工具组

Clip washer and cover

Snap a clip washer into the groove in the shaft behind the bushing. It stops the shaft sliding and keeps the arm and fingers pressed on their rings. Fix the metal cover cap over the parts by bending its ears onto the discs.

此步骤所需材料：