Antique Philco Radio replica speaker plug

thingiverse

This is a replica of the 4-pin plug that many Philco radios from the 1930's used to connect speaker cable to the chassis. Examples include the Philco models 20, 70, and 90 from 1931. Secure parts together using two half-inch 4-40 screws with nuts. Cut three lengths of 4mm OD brass tube, each 0.65" long, for the pins. Use a carborundum wheel on a Dremel tool to cut the tubes. To flare one end of each pin, place it in a pre-drilled hole of an aluminum block so that the back end sticks out and hammer a steel punch into the exposed open end. You can purchase antique-replica cloth-covered 3-conductor wire from Radio Daze LLC. Insert wires into the tubes and solder before installing them in the plastic parts. Secure the cable within the assembled plug using a small, narrow cable tie. Print the components using brown ABS. For the rear piece (speaker plug 3), don't use a brim. Use only about 10% support to fill in the interior and around the rim. Scrape around the rim to remove the support and allow the pieces to nest together. Needle nose pliers work well to clear the interior support. The front piece (speaker plug 1) also needs support for the screw insets, but that's easy to remove. A brim is OK for that part, and for the middle part. It should be clear from the exploded view and photos how it all goes together. I designed this because I purchased a Philco 20 that was missing its speaker. Original speakers of that era are expensive and can be hard to find. Adapting a modern speaker is much more fun, even if the cost is nearly the same and requires more time. A modern (permanent magnet) speaker of the correct size can be adapted by adding a small impedance matching transformer. A Bogen model T-725 from Amazon works well for this purpose. You'll also need a coil of the correct inductance and resistance to mimic the original field coil. I plan to design and 3D print a coil form and coil winder. If they're done and working, I'll post them.