Bunnell C.Q.A. Relay

10      The dimensions of this relay are given as 7.5 by 3.5 inches, which is indeed compact. The typical main line relay measured 8 by 4.75 inches. The "spectacle" frame takes its description from a pair of eyeglasses; the magnets protrude through the "lens" opening.

      The slate base gives the CQA relay a classic look, but two things give it away as a modern style instrument. These are the armature spring tensioner and the wire connectors. The connectors were mentioned in reference to the sounders on page 8. As for the tensioner, the armature spring is adjusted, of course, by varying the tension applied to a string wrapped around the tension screw and tied to the spring.

      The classic spring tensioner was the Extension Adjustment, in which the tension screw was heln a horizontal rod which could be positioned in its own holder either closer to or further from the armature. This "old style" tensioner was used on other models of Bunnell's main line relays which were offered alongside the CQA.

      In contrast, the tension screw of the CQA is simply held vertically in its stand. While the design has been simplified and improved, it lacks the old instrument flavor of the Extension Adjustment.

      The nameplate is of metal, and has the resistance of the relay stamped on it. This type of nameplate was also used on some of Bunnell's wood-based instruments.