Jumbo four-pin bayonet base

The four-contact Jumbo bayonet base combines four pins in a square with a side retaining feature. The bayonet is not another contact: lug position, body rim and terminals must be recognised together. Jumbo alone does not describe every large four-connection base.

The drawing gives a 24.7 mm pin circle and a directly dimensioned centre spacing of 17.5 mm. This explicit distance is retained rather than replaced by a calculation from the rounded circle diameter. The square arrangement and bayonet references distinguish it from bases with the same pin count but different geometry.

Pin diameter is 4.76 ±0.08 mm, with limits of 4.68 and 4.84 mm. Maximum stated length is 8.2 mm. The body has a diameter of 46.7–47.4 mm and a height of 35.4 mm. Illustrated overall height is 42.1 mm, with a solder reference. These describe the construction shown, not the chassis or female contact springs.

Medium, Large, Extra Large, Jumbo and Super Jumbo are not one family scaled proportionally. Pin diameter and length, centre spacings and retention must be checked for the actual construction. No dimension is assigned to another base merely because its name suggests a similar size.

The family's introduction date is not established here. Sockets intended for Western Electric or Eimac versions likewise require comparison of the particular construction. Geometrical fit does not determine valve pinout or electrical operating conditions.