Radio Constructor   Magazines   Valve Radios   Transistor Radios   Military Radios
  My Workshop   Portable Radio Index   Manufacturers Index   Radiograms-Record Player   Crystal Sets
  Links   Component Data   Getting Started   For Sale and Wants    EMail   

Bush BAC 31 Mains/Battery Portable

Bush BAC 31 From 1953 a Bush BAC 31 battery/mains portable.
Bush BAC 31 Chassis A view of the two chassis mounted within the case.
Valve lineup DK92 DF91 DAF91 DL94 and the mains power unit uses an EZ41 valve.
BAC 31 Chassis after repair Repair. The first switch on after checking for short circuits in the power supply unit produced nothing, not even hum.So after checking that the powwer supply was working the chassis was stripped from the cabinet.
Measuring across then output transformer revealed no open circuits but on closer examination the speaker cone apperared damaged.
Once the speaker was removed a tear in the cone of 2" was seen and the soldered connection to the speaker coil was observed to be broken.
After repairing the cone with tissue paper and PVA adhesive the speaker coil was reconnected and the speaker tested before reassembly back into the cabinet.
On connecting the power once again a mains hum was apparent but no signals. Suspecting the decoupling capacitors I started with C22 (The yellow capacitor in the adjacent photograph ) the AF coupling capacitor. This was changed as it was showing signs of wax running. On reconnecting the power the set now produced sound on both Medium and Long wave.
Apart from a cabinet clean the set works perfectly.
below is the circuit diagram for BAC 31 and the Type 42 Power Supply Unit.

BAC 31 Circuit Part 1 BAC 31 Circuit Page 2


Last updated 9.7.2006

2003-2006 © Maurice Woodhead