Replacing Filter Capacitors on the Drake R-4B

Daniel, W6SPC, has a great idea for replacing electrolytic filter capacitors on the Drake R-4B receiver (especially pertinent now that Drake is phasing out servicing for its older gear and parts are becoming less available--Ed): Quad filter capacitors are scarce or no longer available, and the available space below the R-4B chassis rules out using four single capacitors. I installed four singles on a 5-pin plug in the place of the quad unit, however (see drawings, below), and it worked out just fine! A socket was installed in the old chassis hole and wired to connect to the replacement capacitors. Then, wire the individual capacitors to a mating 5-pin plug and you have a four-section filter capacitor. Older-style plugs and sockets like the 5-pin unit I used (or other pin configurations, such as octal--Ed) often are available very inexpensively at hamfest flea markets. The ground plate on the plug--used as the common or negative capacitor terminal--was cut out using the outline of the old capacitor mounting plate. A locking ring holds the plate in place. While I installed my unit in a Drake R-4B, this idea is applicable to any older gear that calls for a multiple-section filter capacitor can.--Daniel Mackintosh, W6SPC.

Image: All capacitors now are mounted on a 5-pin plug (Amphenol 86CP5 or similar).

All capacitors now are mounted on a 5-pin plug (Amphenol 86CP5 or similar). The 5-pin socket fits into the hole in the R-4B chassis that's left when you remove the old filter capacitor. The pins on the socket now are used as terminal points.

Image: Installing the socket in the R-4B.

Installing the socket in the R-4B meant installing a spacer under one side of the audio output transformer to accommodate one side of the socket. Also, the headphone jack will have to be oriented as shown.

Image: I wired up the new 5-pin socket as follows...

I wired up the new 5-pin socket as follows, installing the 1 kW resistor between pins 1 and 3 of the socket:

Pin 1=20 m f
Pin 2, 3, 4=100 m f
Pin 5=ground to chassis