Motorola B3-1E AM/FM Radio (1960)

December 18, 2016
Kihwal Lee, K9SUL

Service manual

It is a typical AC/DC radio, but is a bit unusual radio in that the audio power amp is 50C5 push pull. It sounds great and has ample volume.

  • HCC85 17.5V heater dual triode, FM RF amp, converter (output 10.7MHz)
  • 12BA6 1st IF amp 10.7
  • 12BA6 AM IF (455kHz) amp, 2nd FM IF amp(10.7)
  • 12BE6 AM converter
  • 12AU6 FM limiter, AM detector
  • 12AL5 FM ratio detector
  • 12AX7 AF amp, phase inverter
  • 50C5 Two for PP audio amp

    The tubes are all marked as Motorola. The actual manufacturer is RCA. Only the 12AX7 needed to be replaced. I also added a fuse. The circuit is built on a thick double sided printed circuit board with through hole plating.