Bush BAC31

s/n 141/107080





underside of chassis prior to capacitor replacement

Bush BAC31 s/n    "All Dry" battery portable designed to be used with an optional AC only power unit Type 42. This model was introduced in 1953 and is the first post war Bush portable radio designed for battery or mains operation. Long and medium wave working UK 1953/4 Original cost 13 4s 4d plus mains adapter (a 3 accessory)

It is is a four valve, battery operated, portable super heterodyne receiver, incorporating a frame aerial and covering the long and medium broadcast wave ranges. The valves employed are of the Mullard Miniature series,: DK92, DF9l,  DAF9l, DL94 feeding a P.M. speaker of 6.5 ins. diameter. Adjustable iron dust cored coils, are used in the oscillator and |.F. circuits. For operation on A.C. mains a Power Unit Type 42 will be required, which is designed to fit into the cabinet of the receiver, thus affording means of operating the receiver from batteries or A.C. mains supply as desired.

Bush used wood for the case of the model BAC31 which unlike previous models which were housed in painted Bakelite cases. The styling of the BAC31 is similar to the post WW2 Roberts the P4D and P5A, Vidor and the Pye New Baby Q portable. Common features include hinged rear door and the flap to cover the controls when not in use.

DK92. l.4V .05 amp.
DF9l |.4V .05 amp.
DAF9l l.4V .05 amp.
DL94 2.8V .05 amp.

90 volts for H.T. and 7.5 volts for L.T. Recommended batteries being Ever-Ready Batrymax Type B107 for H.T. and Ever-Ready AD3l for L.T. supplies.

The receiver is designed so that it may be operated from batteries and or A.C. mains supplies. To enable mains operation to be used a Power Unit Type 42 will be fitted inside the cabinet with space being left for the batteries at the bottom of the cabinet. The power unit and the receiver are equipped with four pin plugs and mating sockets so that the double pole switch on the volume control can be used to interrupt the mains supply or the battery supplies depending upon the position of the 'Battery/Mains' switch on the power unit.

This is one of three radios which belonged to Paul Ogden who never got round to fixing them and when I received this one it was not working. The wooden casing had many woodworm holes on both the inside and outside but otherwise appeared superficially to be in good condition. After removing the chassis and the frame aerial the the holes were injected with woodworm killer fluid and those on the outside filled with fine white decorators filler which worked very well and the holes are now almost invisible after touching up with water colour paint and finally clear shoe cream.

The first problem I encountered was that the socket on the receiver had broken contacts so there was no reliable connection between the mains unit and the radio. The next was that only one of the switches on the volume control opened and closed correctly, this was  cured by drilling a small hole into the casing of the switch assembly and injecting switch cleaner fluid. Several of the rubber insulated wires were replaced and the faulty plug and socket wiring to the switch was bypassed to enable the set to be operated permanently from the mains supply.

With the set energised I was still unable to get a squeak from it even though the loudspeaker and transformer proved to be OK. I measured the HT and LT voltages from the power supply and found them both high which lead me to discover that the filament of the DAF91 was open circuit! Fortunately I had a spare which when inserted caused the LT voltage to drop to about 8 Volts and for some noise from the speaker but the set was still essentially dead. A finger on the grid of the output valve produced a loud hum which at least proved the output stage was working.

I decided then to check the capacitors, the first checked was the large 0.5mFd wax covered capacitor mounted above the chassis which when disconnected improved things considerably. An aerial touched on the tuning capacitor brought in faint tunable signals. I removed the internals and stuffed the casing with a modern 0.47mFd 400V working one.  After testing of a couple of others I decided to change the rest. This was not straight forward due to the crowded layout below chassis so I had to remove the variable tuning capacitor and cut them out and replace them one by one with Mullard C280 capacitors that look like liquorice all sorts. Now after straightening the front panel and re-assembly the set now works well and I replaced the Bush logo which Paul Ogden subsequently found and posted on to me.

c280 caps                                          bush logo

Bush rose from the ashes of Amplion who made speakers for British Gaumont cinemas and thus had links with the film industry.The radios were advertised in Gaumont cinema foyers as "A Gaumont British Product".  Murphy experienced problems keeping at the forefront of technology and lost creditability with their dealers, many of which changed over to Bush. At some point Murphy became part of Bush and the company trade as Bush - Murphy in Chiswick, London. In 1945 because of their links to the film industry, Bush Murphy became part of the Rank empire and changed the name to Rank Bush Murphy (RBM).  A new satellite factory was opened in Plymouth in 1949. During the mid 70's (When they were one of my major customers! I worked then for RCA Solid State having previously been with both Mullard & STC) ) they moved the entire operation to Plymouth.  In 1972 the name was changed again to Rank Radio International (RRI). Following several years of mounting losses  they tied up with the Japanese to become Rank Toshiba in 1978. This lasted just 3 years, and in 1981 finally folded. Toshiba became sole owner of the Plymouth factory. The Bush name now belongs (along with Alba) to an importers in Barking, E London.

Thanks to Colin Boggis for this information

Have a look at this site for a very comprehensive and interesting history of Bush radios http://www.bushradio.co.uk/