Drake R-4A R4B Product Detector Upgrade

The dual-diode product detector in the 11 tube Drake R-4A (aka R-4A "late") and the Drake R-4B has poor dynamic range, promoting distortion on AGC attack. This manifests itself as annoying clicking and popping on strong signals.  A modern adaptation of the former Sherwood board, this active Gilbert-cell detector will correct this deficiency.  Installation takes only about 30 minutes but does require basic soldering and schematic reading skills.  Board size is 30mm x 25mm