Heads Department
Looking back on the early days of videotape, it still seems a miracle to many of us that anything worked at all, let alone the fact that we actually made programmes! So much was in its infancy - it was not neccesarily guaranteed that a recording made on one machine would play well on another, and, in an era of cut editing, physically splicing the tape, there were problems cutting together recordings made on different machines. It was quite common for a specific video head to be moved from machine to machine to make sure that a programme recorded over a period of time would actually be able to be spliced together.
There were also problems of quality control and uniformity in head alignment - the memos in the Head Wear section give some insight into these difficulties - and so a specialist Heads Department became essential. Dave Moody tells the story.

A Brief History of VT Heads Department
(some of it before my time) by Dave Moody

When I joined VT in 1970, some of the previous generation of VTRs were still in use e.g. the last VR1000 (relegated to tape servicing), RCA TR22s, and I was told stories of the days when you only replayed tapes on the machine that recorded them, or even sent the video head with the tape to enable a replay. Things had moved on considerably since then, but everything from Low Band Monochrome to High Band Colour was still in use throughout the BBC, although 405 line output was only produced at the transmitters or for standards conversion. The evolution of video heads described up to then is by word of mouth from my colleagues.
By the mid 60s, the increase in quad vtrs with the arrival of the prototype VR2000s, and the relatively short video head life being achieved by the MK IV assembly, led to an increasing logistics problem in tracking the condition of each head assembly and maintaining a supply of useable new assemblies.
Ideally each machine needed 3 head assemblies: one in use, one spare, and one away being reworked. Operators routinely measured tip projections but this was inaccurate and often damaging to the tips. The very short head life experienced made the video head assembly the major source of unreliability for the machines with unexpected failures. The reasons for such short head life (around 50 hours) were most likely: the varying gap depth supplied by the head manufacturer, varying abrasiveness of the stock being used, local humidity variations and excessive re-contouring of the tips due to operational guide adjustments for best replay. MK IV head cores (tips) were two part construction (ferrite body with Alfecon pole face to prevent saturation) and relatively inefficient with windings spaced from pole face.
The very high cost of reworks warranting a QC of new assemblies and a growing requirement for closer mechanical tolerances to enable tape interchange between machines (from two different manufacturers by then) led to the need for a specialist ‘heads engineer’ on each shift. I believe that the first two were Ted Taylor and Chris Laid. When Ted later left the BBC, Chris moved to days, joined eventually by Bob Seaward (Rupert).
Mark 10 HeadThe immediate engineering challenges were colour recording and interchange electronic editing, for when BBC2 started a full colour service in July 1967, which were very dependant on improved video head performance. This also coincided with the introduction, by Ampex, of the MK X video head assembly (picture right) for the VR2000.  Mechanically similar to MK IV, this offered improved single construction Alfesil tips, better rotary transformers, an optional head preamplifier (with Nuvistors and shorting screws to reduce gain as heads wore down), and tighter mechanical tolerances. 
Brian Jenkinson (Investigations) worked with tape manufacturers (like 3M), improving the performance of the tape supplied resulting in eventually Scotch 400, while Chris worked with the video head manufacturers/re-workers on improving consistency and tolerances for compatibility of recordings.
Alternative reworks to OEM were tried for the MK X. Videomax and RCA (Jersey) were used along with Ampex reworks from Nivelles and Colorado Springs.

The mechanical maintenance team had superb ‘toolmakers’ who made jigs for very accurate measurement of tip projection, drum diameter, and guide radius, all defined in SMPTE RP11 for successful interchange between VTRs. The knowledge that assemblies were undergoing QC, led to reworks of a much more consistency. A similar improvement occurred with tape under B.J.’s QC regime.
The idea of a centreline tape and a reference head, to compare all new stock and head assemblies to, was evolved. VTR Alignment Tapes were available from manufacturers but a whole series was required to set all the machine parameters and they were expensive and there was quite a spread between the various manufacturers. An in-house Reference Tape seemed a good idea as it would be more typical.

Investigations were carried out and a paper was written on a system of pre-alignment of the replay side of the quad machines, using a centre line (reference) tape, to enable a matched ‘standard chrominance’ recording to be made by each machine, when correctly adjusted, routinely every 20 hours.
This was to become the ‘Constant Chrominance Optimisation’ procedure adopted throughout the BBC and many other organisations. Many hours were spent measuring critical parameters on many machines to arrive at the Reference Tape to be used for alignment. A further advantage was that it was made on current stock and more representative of machine/ tape performance and could be used to set all machine parameters. The legacy benefits organisations like the BFI, who today still replay many quad recordings with little need for adjustment between tapes. (Click here Click to see a paper describing this process - Adobe pdf)

By late 1960’s machines were becoming more intensely utilised and the only available time for this pre-adjustment was after closedown or before the start of the early shift. The Heads shift thus started at 05.30 a.m. and all engineering operators had a 3 months ‘Heads attachment’ to carry out a routine optimisation of all the quad vtr’s on a regular rota. We can all remember optimising to the soul music from ‘Radio Laid’ on the ring main from the Heads Room which seemed to move around every few months.
Originally located opposite the main tape store, it moved into Film Recording (Area 2) then finally to the dressing room just outside Area 2. It was on ‘Heads’ that operators learned the mysteries of the FM recording system and the manifestations of distortions caused by misalignments of the video head assembly such as: azimuth, coplanar, wrap around, quadrature, once around, tapered gap, binding transformer, to mention but a few.

By the early 70’s the VTR count at TC was in excess of 30 including VR2000, VR1200, TR70C, and AVR1. The Constant Chrominance Optimisation method meant that programmes could be started on one machine and continued later on another with minimal adjustment needed for matching, reducing lineup.
Mechanical variations between machines was reduced e.g. capstan speeds matched by plating and machining flywheels to a high tolerance. Deck alignment was routinely checked by the mechanical maintenance reducing residual head error contributions from the tape path.
All new head assemblies (including those for the Regions) were QC checked on arrival from rework and many repaired in service by swapping components (e.g. pre-amps, control track heads) with worn heads being sent for rework. All of this and improvements in climatic control in the area led to an average video head life nearer 200 hours. Further reliability was provided by a centralised air compressor with automatic backup.
Audio assemblies were routinely checked for inductance and the pole pieces re-profiled and reprojected every 500 hours, improving the LF performance and prolonging the life, compared to allowing them to wear until contact problems caused rejection.

Mark 15 headIn 1975 the AVR2s arrived further swelling numbers of vtr’s as Area 2 was taken over. The MK XV head (picture right), although mechanically similar to the MK X, was equipped with a dc motor, requiring commutation from the head drive. The pre-amp was back in the machine, under the hood with the triac control for the reels (picture below). Around 1977, Spin Physics (a Kodak company) offered a MnZn ferrite pole tip refurbishment with a 1000 hour head life guarantee. The high efficiency tip material had a definite advantage in a lower wear rate but was more likely to chip or break. The initial construction was to sandwich the ferrite in between two glass cheeks, but the differential wear rate between the two materials allowed the bond lines to eventually become proud and cause overheating of the tape binder, particularly with Agfa tape, and cause oxide stripping. The tip was redesigned with just the ferrite and we were regularly achieving the 1000 hours on an AVR2, with a record, as I recall, of some 2500 hours.

Under the hood of an AVR2

CMC who had provided us with ‘metal’ reworks for the MK X and TR 70C head assemblies for several years previous, was persuaded to offer a ferrite rework. There was initially a compatibility issue with recorded chroma levels on a VR2000 but this was solved initially with in-line filters to the RAPA’s, which later were incorporated into the head assembly. Resulting head hours achieved were less impressive than on the AVR2 but often exceeded 1000 hours with a warranty of 500 hours. They then also offered the AVR2 rework in ferrite (as did Ampex) and also theTR70.
Although they have changed their name to AheadTec, they (CMC) still offer reworks today and BFI are achieving 500 hours with archived tapes that have become very abrasive with age.
Ferrite became the preferred rework, although metal heads were still used, until quad was replaced by C Format in the early 1980’s.