Draft:MCR21

MCR21 was the name applied to an Outside Broadcast van delivered to the BBC during the 1960s.

Television Outside Broadcasts have evolved alongside technical developments of Television production and this particular article will focus on one example of OB technology from the 1960s and its restoration.

Introduction
MCR21 is a complete television studio on wheels, nearly 25 feet long (7.6m), 8 feet wide (2.4m) and nearly 12 feet high (3.6m). When in use, the electronic equipment develops a lot of heat, so the vehicle has air conditioning and 3 large roof extract fans (the very first MCR had none of these, and the staff had to work for hours in temperatures of over 100 degrees F (38 C)). The original equipment included Four cameras (Pye Mk6), A 10 channel vision mixer (BBC design), seven picture monitors, a Pye 20 channel sound mixer with it’s own tape recorder, test equipment and synchronising generators – all as described below. v

MCR21 (Mobile Control Room 21) was the designation given to a van equipped for providing TV outside broadcasts. It is one surviving sample of 10 similar vehicles manufactured by Pye, at the time based in Cambridge, UK, purchased by the BBC during the 1960s.

The vehicle was built on a Commer Chassis C762 having a 6 cylinder petrol engine and 4 speed gearbox. It was first registered as 388 EXH on 12 November 1963.

The vehicle is now owned by the Broadcast Television Technology Trust (BTTT), a charitable trust which has been formed to restore and preserve historic broadcast television equipment for public display and education. Restoration of MCR21 is the first project to be taken on by the trust.

Engineering Crew
Engineering Manager, Lighting Director, Vision Supervisor, Vision Engineers, Sound Supervisor, Sound Assistant, plus Rigger-driver Supervisor and Riggers.

Production Crew
Producer, Production Secretary (PA), Researchers, Commentators, Interviewer, Floor Manager, Runners.

Production Desk and Seating
MCR21 has a 'Transverse' layout across the vehicle which was the convention at the time. Viewed from the right side of the vehicle: the PA's desk, vision and sound mixers then the EM's desk. There were four principle seats: the PA (Production Secretary) VM, the Vision Mixer who was often the Director, the Sound Supervisor, then EM (Engineering Manager). There was also a bench seat across the rear and a small drop-down seat for the Lighting Director. In front of the production desk were four seats for the Vision Supervisor and Vision Engineers. Up to eleven or twelve people might be working in the production area.

Later and larger vehicles adopted a longitudinal layout with the production desk being installed along the vehicle length.

BBC Outside Broadcast numbering schemes

The DVLA - the registration number is 388 EXH and was issued on 12 November 1963

The MCR number: the first OB vans or scanners were built before the war and were numbered MCR1 and MCR2. After WWII numbering was continued up to MCR28, which was the final monochrome scanner. With the advent of colour TV the BBC started again at 1, however this time with a 'C' prefix, the first colour scanner being CMR1 and so on.

The Transport Fleet Number

In addition to the MCR numbers there was a 'fleet number'. This was composed of a letter taken from the first letter of the chassis manufacturers name and the three numbers from the registration numbers. Accordingly, the fleet number for MCR21 was C388.

The Local Unit Number

If this was not enough there was also a local number. This number tended to change and could be allocated to different vehicles at different times or locations.

MCR21 was variously known as Unit 1, LO1 or LO21. Over the years a least four different vehicles known as LO21, MCR21 being the first.

Sound Systems

The sound desk installed in MCR21 was made by Pye Ltd. from modules in their 'Broadcast Audio Equipment' range. The idea behind this was that sound mixer installations could be made up by combining a number of standard units selected from the module range.

These formed a twenty channel sound mixer system with three groups of ten, four and six banks. A complete system with monitoring, programme outputs and talkback, all to BBC requirements was made up for MCR21 complete with amplifiers, PPM's, faders, power supplies, reserve battery supplies, tone generators plus a telephone system with ring generators.

A remotely controlled two channel 1/4 inch tape recorder was included for recording or effects replay. There was also a BBC designed audio line identification unit types RC4/1

Failure Protection

The sound system has automatic battery backup so that the programme could continue in sound only in the event of total power loss. The internal unit lighting and talkback systems also have battery backups. The video system is arranged to be resilient against failure, with independent routes from cameras to transmission output.

Vision System

A BBC designed ten channel vision mixer type MX1/501 is installed. It has A & B cut banks and Wipes. The Vision Mixer control panel has A & B cut rows and between them is a paper strip to write notes on, to the right are twin faders. On the extreme right is a set of preview buttons. Above is a function switch for Insert/Fade/Wipe and top centre the wipe pattern selector buttons.

When this mixer was designed in the early 1960s it made use of solid-state diodes as the switching elements; the first time that this kind of technology was employed within vision circuits. This cutting-edge design was further developed for use on colour TV and was in service in a range of BBC studios and outside broadcast vans into the 1980s.

The Vision Matrix
The Vision Matrix and the Musa Jackfield were new facilities, used for the first time in OB vans. The matrix and to a lesser extent the jackfield could be used for routing video signals. Similar in some respects to a small telephone exchange, for instance the feed to the commentators monitor could be switched between transmission, off air or reverse vision.

Monitors
Six 14 inch picture monitors are installed, one dedicated to each camera and two switchable preview monitors. Each monitor has an associated waveform monitor. A 17 inch monitor is used to show the transmission output from the vision mixer Additionally there are two Tektronic 515A oscilloscopes for measurements plus a Peto Scott 8 inch monitor.

Vision Control
There are two desks for use by the vision engineers which are attached to the front of the monitor stack. Both feature two camera OCPs (Operational Control Panel), one also has the vision supervisors panel the other has space for the controls for an optional 5th camera.

Cameras
MCR21 was originally fitted with four Pye Mk6 black & white cameras, constructed to BBC specifications. These used the Image Orthicon tube which provided the best pictures possible at the time of manufacture. Each camera could be fitted with up to 4 lenses in a rotating turret and the camera also featured a high resolution viewfinder.

Provision was made for an optional fifth camera and for external cameras hosted elsewhere. Comprehensive talkback facilities were provided - production talkback, engineering talkback, programme sound and cues.

A complete camera channel consisted of four main parts: the camera head itself which connected via a multi-core cable to the CCU (Camera Control Unit) inside the OB van. In turn, the CCU was connected to an OCP (Operational Control Panel), all were powered by a PSU (Power Supply Unit)

Ready for BBC2

MCR21 was designed and built ready to work in the 405 line TV system, or the 'high definition' 625 line system. BBC2 started on 20th April 1964 using the 625 line system.

Technical Tailboard

All sound, vision and camera connections signals are routed through the Technical Tailboard on one side of the van.

Video signals are on SO235 connectors; sound signals are on XLR connectors. Additionally there are multi-way connectors for up to eight audio circuits in one cable and four camera control cable connectors, type BICC Mk4b.

Power Systems

Power Tailboard inputs and outputs:

At the rear there is a locker with the power inlet panels. This has the main 80 Amp. power input connector and a second standby connector with interlocked changeover switches. These large brass connectors were made by BICC. Additionally there are several Niphan mains output output connectors for supplying power to commentators or interview positions.

It was the BBC's practice to use power extended from the Outside Broadcast van to these remote locations so that full control of them is possible, rather than some potentially unreliable local power source.

Internal Distribution:

The main input cables go to an internal circuit breaker and fuse panel, where it is split into four main circuits; three technical supplies A, B and C which have automatic voltage regulators and D, which is an unregulated supply to feed fans, heating etc. These four main circuits are then sub-fused to feed final circuits.

It was the practice in 1963 to fuse both the line and neutral cables. The fuses have been retained for originality in appearance but they are not in use.

The Vehicle

MCR21 was the third unit of ten to be built to a BBC specification, TV90. The coachwork was by Marshall's of Cambridge and the technical installation was by Pye. These ten Outside Broadcast units, the 'main fleet scanners', formed the mainstay of the BBC's fleet in the middle 1960s until the advent of colour TV.Seven were allocated to London and one each to Cardiff, Bristol and Glasgow.

Chassis and Engine

A Commer chassis type C762 powered by an OHV six cylinder 4.75ltr Rootes petrol engine engine with four speed gearbox and vacuum servo brakes. There was no power steering! MCR21 is 28ft 8ins long, 11ft 9ins tall and 8ft wide.(Approx 7.6m x 2.4m x 3.6m).

Coachwork

The coachwork was carried out by the specialist firm 'Marshall's of Cambridge' and is almost entirely aluminium apart from the rear quarter panels and some structural parts supporting the scaffold side poles. There are 5 doors and 7 skirt lockers around the sides. The roof is decked with teak planking and there are three roof-mounted extractor fans.

 Environmental Control

An air conditioning unit is installed in the rear looker cooling the production area. The technical areas to the front have air inlets in the floor and three roof extractor fans. Each operating station has a foot warming floor heater and anti-condensation heaters are installed in the base of the monitor stack.

Refurbishment

The work of refurbishment of the vehicle continues, conducted by a team of volunteers













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