Pilot Under Glass Tube Radio

Tom's Designer 1625 Regen Radio

Looking for a truly unique gift for Christmas, birthday or any day? This one-of-a-kind creation is just the ticket especially for that special someone who appreciates fine craftsmanship and originality in antique radio lore. This radio marries the top end archtop guitar builder skills with electronic schematics from the 1920’s and 30’s to create a special tribute to both.

Regenerative circuits were first developed in the 1930’s and the schematic followed for this set came from Dave Schmarder. A very early day PILOT variable capacitor is combined with a coil wound on an Amidon toroid form to provide the tank and a trimmer capacitor set at 30pF couples the antenna to it. The PILOT capacitor was manufactured to allow a more even tuning of the broadcast band rather than a standard capacitor design that bunches most signals to the top half of the dial. This v ariable capacitor was completely disassembled and refurbished to new condition and then treated with a coating to resist tarnishing. The coil was wound using 176/546 litz wire to an inductance value of 155uH since the trimmer and tuning capacitor had a total capacitance of 455pF. A small amplifier and speaker were installed to avoid the encumbrance of using headphones to listen with.

With a variable capacitor of this magnitude and beauty being used a method of showing it off had to be conceived and a back of clear Plexiglass was the answer. A 1625 power beam tube dominates the left end of the radio and features massive solid brass rods for the plate cap connection to the circuit inside. I understand these tubes were widely used in aircraft radios during WWII and this one continues to ‘fly high’! All control knobs are also solid brass with the larger one being the tuning knob which also turns a belt drive to the tuning dial at the left end of the front panel. A gorgeous antique glass crystal houses a Zenith dial face manufactured in 1936. The dial bezel was made of black walnut.

The curvy black walnut cabinet presented several challenges in fitting appointments to these undulating surfaces that included the tube’s base collar, the speaker grill and the speakers mounting platform for attachment to the inside of the cabinet wall. Guitar making techniques were employed to assure exact fits in every case. After final sanding all wood components were stained, sealed and finished with multiple coats of nitro cellulose lacquer.

Power for the unit is supplied by a 12vdc wall wart transformer so no dangerous or multiple voltages are required. All that is required is an antenna and ground source.

Tom's Designer 1625 Regen Radio, side view
Tom's Designer 1625 Regen Radio, side view
Tom's Designer 1625 Regen Radio, rear view