[David Dunlop]

The last set of components to be removed from the coil case are the two brass Mounting Plates on either side of the case bottom, that support the four Airloc Studs which are used to attach the Coil, Aerial Tuning No. 2 A to either the top, or right side of the Carriers No. 4 for the 52-Set.

Each of these plated brass Mounting Plates are fastened to the coil box by three plated brass 10-32 RH slotted machine screws. On the left hand side, these three screws are all one inch in length, with matching plated brass Shakeproof washers and hex nuts. On the right side Mounting Plate, the same one inch long hardware sets are used for the back and centre positions. In the front position on this side, a plated brass 10-32 x 1-1/4 inch RH, slotted machine screw is used. The extra length is to allow for the fitting of the brass grounding strap connected to the aluminum front panel of the coil assembly. But the hardware for these plates does not end there.

Each of the six mounting holes is 3/16-inch diameter and passes through the 3/8-inch pine board bottom of the case, as well as the 1/2-inch square pine strip reinforcement found mounted in the corners of the case. From the inside, a 13/32-inch diameter countersunk hole has been drilled down into each hole 3/16-inch deep. In the bottom of each hole, in both tuning cases I have available, I have found a plated brass 10-32 flat washer with a 3/8-inch OD. These are needed to prevent crushing of the wood when the Mounting Plate hardware is installed. The countersunk holes appear to have been factory painted and I am not sure if these washers were originally fitted with dab of glue, or have simply stuck to the painted surfaces of the holes after 80 years of close contact, but not one of them was willing to fall out on its own. Each had to be carefully popped out with a thin awl.

Getting this hardware out to remove the two Mounting Plates is challenging. When the hex nuts were originally fitted, they end up just below the surface of the wood in the countersunk holes, so are inaccessible by means of a spanner or 1/4-drive socket set. This took a bit of thinking on my part to solve.

Ideally, to keep the hex nuts from rotating with a potentially sticky screw, the hex nut needs to be held in place directly. I was hoping my various parts bins might have held an old bicycle tyre inner tube from which I could punch out a nickel sized disc of rubber. No such luck. But I did find a scrap piece of canvas from which I cut a one inch square pad. I then wet it just to the point of being slightly damp.

With a little experimenting, I found that the 1/4-inch socket in my quarter drive set was the perfect size to fit freely inside the countersunk holes in the wood, while also fitting freely over the tip of the machine screw. By placing the damp bit of canvas over the hardware, I could then fit the quarter drive setup on top so the rim of the socket was resting fully on the face of the hex nut. I did this with the coil case resting on one side at the end on my bench just far enough the Mounting Plate assembly cleared the bench and the side of the coil case was flat on the surface of the bench. In this way, with pressure applied to the faces of the hex nuts, all the three sets of hardware on the left side Mounting Plate, and the back two sets on the right side, all came apart easily.

The front screw set on the right side Mounting Plate is the 1-1/4 inch machine screw that has the additional Shakeproof washer and hex nut set holding the brass grounding strap for the front panel in place. With this first hex nut/washer set removed by conventional means, the brass ground strap can be removed to expose the recessed second hex nut and lock washer. The 1/4-inch socket was deep enough that with the canvas snugged down on the part of the hex nut facing into the coil case, this set of hardware also came off easily.

The coil case now sits free of all its fittings, except for the green felt pad glued to the bottom.

My apologies that this post turned into such a ‘Natter’.


David