Modifying my R-4C

Process phases

Factory original R-4C
Original R-4C
R-4C half modified
Modifying R-4C
R-4C totalmente modificado
R-4C completed
Top view of the R-4C with the new filter of the first FI installed
Top panel view
Rear view of the R-4C with the DDS inputs installed
DDS wiring connectors

Final details

Schuko adapter used in the entire Drake line so as not to cut the original plug
Schuko adapter
FCN PRO filter with 6 Khz bandwidth and shape factor < 4
FCN PRO filter shape factor < 4

Upgrades on my R-4C

  • Modification FCN PRO first mixer.
  • Modification FCN PRO second mixer.
  • Modification FCN PRO product detector.
  • Install 1 FCN PRO filter on the 1st FI (BW 6 Khz) (Replaces the original BW 8 Khz).
  • Install 1 FCN PRO filter on the 2nd FI SSB (BW 2.1 Khz) (Replaces the original BW 2.3 Khz).
  • Install 1 FCN PRO filter on the 2nd FI AM (BW 6 Khz) (Replaces the original 2 W resistor).
  • Change the 240 VAC 60 Hz power supply transformer for another 230 VAC 50 Hz transformer to avoid excessive heating.
  • Install 5 miniature and compact stabilized DC 6.3 V and 3 A power supplies to feed the tube filaments.
  • Install a silent turbine to cool the 230 VAC 50 Hz power supply transformer.
  • Install 3 voltage stabilizers of 14 VDC, 11 VDC and 10 VDC +/- 1mV to power the VFO, the crystal oscillators and the product detector.
  • Install a 150 VDC voltage stabilizer to power the plate and grid circuits of the valves.
  • Install AF circuit of 4 Ω and 5 W.
  • Install DDS IN and MUTE input connectors to connect the VFO DDS R-4C.
  • Clean switch contacts and valve sockets.
  • Change electrolytic capacitors and resistors with altered value.
  • Adjust all RX parameters and calibrate oscillators.
  • Mechanical gear adjustment and analog dial knob.
  • Cosmetic restoration (Change screws for identical stainless steel ones, polish buttons and legs, put new rubber stops on the legs, paint the white stripes on the controls, change dial and smeter lamps, change filters dial and smeter window blues, etc).
Power supply for the new modified R-4C
Power supply for the new modified R-4C