Author: radiophonic museum
NON-BBC isolation boxes
Something biblical about these effective transformer balanced isolation boxes, built by the BBC for everyone else.
Great for reducing hum when nothing else works..
BBC A.C. Test Set
Cool looking BBC test set dating from the 60s which can still occasionally be found lurking in dark cupboards and behind installations throughout the Corporation.
A handy meter for independent level testing.
BBC Type Am6 limiting amplifier
A great transistorised limiter from early in the BBC’s popular Am6 series.
Later varients like the white faced Am6/7 and the Am6/17 made under licence by Neve and Calrec are better known and, as far as music production goes, more aggressive or clinical respectively.
The Am6/3 has the option to internally modify to a softer ‘compression’ slope, but sounds fine as it is.
BBC Transformer design
BBC Type B equipment
BBC Type B modular equipment was introduced in the mid 1950s, to replace the larger and more expensive post war Type A installations.
Based on a smaller and more readily available valve, the ECC81 (or 6060 with lower microphony) the Type B became a familiar sight in many BBC studios across the land, including of course the Radiophonic Workshop. It is surprising that so few appear to have survived!
King of the roost was the AMC/5 microphone amplifier with fixed gain stages of 40 to 70dB. This had been developed from the earlier general purpose GPA/4 amplifier which was also used for microphone applications. Further down the gain chain was the C/9 line amplifier with 10dB in hand.
Amplifiers were attached to specially designed frames, held in standard BBC issue 19″ racks.
Consoles were passive, constant impedance, utilising Painton stud faders and in some instances with quadrant faders, such as at the Radiophonic Workshop as seen here in the capable hands of Delia Derbyshire.
BBC OB Type 9 Loudspeaker Unit
The LSU/11 was a 1 watt, yes 1 watt loudspeaker, with an 8″ Wharfdale driver.
Designed as a compliment to the OBA/9 system, with portability in mind.
BBC OB Type 9 Communication Units
Additional items to the OBA/9 trolley were these communication units for lamp signalling between the operator and various microphone points.
The CMU/10 also provided for a P.P.M. meter which was powered off the OBA/9 rig.
Not currently in use, but looking forward to getting these lit up like a Christmas tree.
BBC OBA Type 8 type amplifier
The OBA/8 system was introduced in 1938. Intended for portable use with war in Europe looming, it was more lightweight then predecessors and utilised a pentode valve for the first time in British amplifier design.
The whole system, designed for self operation, consisted of two OBA/8 amplifiers (one on standby), a passive MX/18 mixer, LSU/1 loudspeaker and comms.
Many units, particularly the MX/18 mixer, continued to find a use long after peace had been declared, in provincial studios and of course the Radiophonic Workshop.
Here is a picture of Daphne Oram with three such passive mixers, which utilised wire wound constant impedance attenuators (and an OBA/8 in the foreground).
BBC OB Type 9 amplifier
The OBA/9 system evolved in the 1950s to replace OBA/8, with a smaller footprint and expanded facilities to meet the demands of outside broadcast engineers as the needs of broadcast expanded.
The whole system was designed to be ‘portable’ of a fashion; consisting of an MX/29 passive mixer, OBA/9 valved amplifiers with high gain and power supply, along with monitoring amplifier and distribution facilities. Ancillary items included a loudspeaker LSu/11 and communication units CMU/9 and CMU/10
