Cathedral 1625 Radio

Cathedral Style 625 Regen Radio

Dave Schmarder is actually the architect of these new cabinet designs since it has been he that continually encouraged (pestered) me to try the idea out. This has been going on for several years and I finally capitulated and am more than pleased that I did. My main concern has been that if a tube set were being constructed the tube would be hidden from view. I have always featured the 1625 tubes since they are so big and robust and downright nice to look at. I still harbor that worry but the overall impact of the cabinets makes it more than worth the loss of sleep. My previous radio using a domed cabinet was an EM83 magic eye set and certainly it was paramount that the tube be visible so I cut a window into the front panel for that purpose. Cutting a window to show a 1625 tube would pretty much take out everything else on the panel with no room left for tuning dials, speakers and so forth.

The cabinet built for this radio stands 7” tall at the apex and is just barely has room for the tube, socket, standoffs and plate cap. A 1 ½” tall platform was required for the 396pF variable capacitor in order to make room for the regeneration potentiometer and the amplifiers on/off/volume pot. This potentiometer had to be removed from the amplifier and reconnected with 8” long leads since the amp itself is mounted on the floor of the cabinet at the far end of the cabinet. It is mounted on 1/8” standoffs to clear the wiring below the chassis.

The tuning dial is a 360 degree SILVERTONE beauty from 1937 and is encased under a 3 ¾” diameter convex glass crystal and its bezel of tiger maple. Both it and the speaker grill are difficult to craft and would be impossible without a metal lathe and a vertical milling machine. The pointer shaft is polished 1/8” steel and is mounted in a brass sleeve that was bored and reamed for perfect tolerances that give a very smooth action. Since this is a 360 degree dial I had to build one pulley 1” in diameter and the other ½” diameter. The first trial tuning only moved the pointer about ¼ around the dial….I had the pulleys backwards! Made me feel pretty silly.

The schematic used was the standard I have used for years from Dave Schmarder. The tank is made up of the 396pF variable capacitor with actually measured 399pF which when added to the 41pF trimmer capacitor used to couple the antenna to the tank dictated the coil be only 165uH. I wound it on a torroid core from Amidon Corporation using 175/46 litz wire.

An extremely wild and mixed example of tiger striped maple was used for the sides, top and front panel of the cabinet. Triple sanding the stained surfaces made the character of this wood stand out very nicely. Finally everything was sealed and finished with several coats of nitro cellulose lacquer that I flatten here in my shop.

Cathedral Style 625 Regen Radio, side view
Cathedral Style 625 Regen Radio, another side view
Cathedral Style 625 Regen Radio, back view