Devil's Twig Radio

This charming radio has many nice features to see. The tube is a sub-miniature 6418 which has filament voltage of 1.25vdc with 10 milliamps. The plate circuit operates on a 12vdc wallwart and with a series of resistors and 1n4004 diodes this same voltage is reduce to a little less that 1.5vdc for the filament. It is always a victory for me anytime I can avoid using batteries that run down and are a hassle to change out.

This little tube has a diameter of only ¼” roughly and the radio is a regenerative set. It has a 50k potentiometer for gain control, a 10-60pF variable capacitor for antenna coupling, a 365pF capacitor for main tuning and a coil wound on a toroidal core from Amidon Corporation using 175/46 Litz wire to an inductance value of 244 µH. A tickler coil was also wound to 10 µH. Actually, I had to wrap the main windings with plastic tape and wind the ticker coil on top of that.

The antenna tuning capacitor was a screw drive adjusting model but I machined a special step-down shaft from 3/8” diameter to ¼” diameter with 7/32” hole bored into the 3/8” section and tapped for set screws that bind on the hex head nut. This way the ¼” shaft can be fitted with a knob for easy operation.

The radio also features a small amplifier and speaker but the confines of the cabinet dictated that the on-off volume potentiometer be removed from the amplifier and fitted with long leads so the circuits board could be mounted where it fit and the pot located on the front panel. There were several such adaptations that were necessary and these made the project very time consuming indeed.

All knobs are solid ½” diameter brass. Three sport 1” diameter ABS plastic skirts (used as binding on guitar tops and backs) and the gain control has a ¼” diameter flamed maple skirt to match the ¼” tube tower base and the speaker grill. The cabinet is 6 ¾” wide and 2 7/8” tall. Highly flamed fiddle-back maple from my guitar shop was carefully steamed and bent to shape then attached to the frame. Everything was carefully sanded, sealed, stained, shaded and finished with satin nitrocellulose lacquer. The tubes ‘tower’ is a section of Devil’s Walking stick from a remote area of New Mexico. It and its base were treated with very flat lacquer that I prepare here in my shop. All brass screw heads were polished to a high shine before use and the overall appearance of this radio is very nice.