I was involved in the technical side of broadcasting in South Africa from 1965 till 1996. It was a fascinating 31 years and I was privileged to see amazing developments in broadcasting equipment. But SABC was not just a user of broadcasting equipment. It was a very successful manufacturer.
The early SABC modeled itself on the BBC which was widely acknowledged as a world leader in excellence, both in production and in the research, development and manufacturing of broadcast equipment. In the 1960s we were importing a lot of equipment from America, Switzerland and the U.K. but we had some brilliant engineering brains in South Africa and they started the SABC manufacturing workshops in Judith’s Paarl in Johannesburg. There we would manufacture from absolute scratch, everything from turntables to tape recorders to mixing desks and even microphones. We even improved on some of the technical equipment we had bought in and some of the SABC innovations were taken up and used by the international community. I will tell more about the things we manufactured in a later article but today I would like to talk about the the master clock systems used over the years by the SABC.
Time keeping has always been important in broadcasting. Listeners want to switch on the radio station of their choice at a given time and hear the program or news bulletin they were promised for that time slot. People also want to set their watches to a universal time signal so that everyone’s watches correspond. It’s important for meetings etc. In the early days of broadcasting, anything within 1 second of the correct astronomical time was good enough.
the effective length that decides its period is the distance from the knife edge to the centre of gravity. ie, roughly to the centre point of the bob. The old Gents master clock had a compound metal pendulum shaft and a bob of a different metal. The bob could slide freely up and down the shaft and the bottom of the bob rested on and was carried by the bottom plate of the shaft. The theory was that on a hot day, the shaft would expand and get longer, thereby slowing the clock down but the bob would expand from the bottom upwards and compensate for the change in the shaft length. It worked pretty well but it was not perfect. As a result, the clock would drift slightly out of time as the weather changed. We at the SABC used to listen in every day on a short wave radio to the time -signals from the astronomical observatory. If our clock was more than 1 second slow, we would place a small weight of about 1 or 2 grams on the top of the bob. This was above the centre of gravity of the pendulum and therefore raised the centre of gravity minisculy. This was just enough to bring it back into time for the day. If Our clock was running a bit fast by the observatory, we would add the small weight to the bottom of the bob, lower the pendulum centre of gravity and slow the clock down a tad. The system worked but it was very tedious.So the engineers at the Judith’s paarl workshops designed and built a system that would electronically listen to the time pips from the observatory and then use a relay mechanism to mechanically place a fairly heavy metal marble onto, or remove it from a platform affixed half way up the pendulum shaft. This then adjusted the effective length of the pendulum and altered its speed. The system worked brilliantly and never needed manual intervention any more.
The SABC ran on these pendulum clocks until TV arrived on the scene in 1973. But TV stations require far more accurate time-keeping than one can ever get from a mechanical device. So the old clocks were replaced by a form of atomic clock called a Rubidium standard. This is a whole nother story and maybe I will get to that in another article. The Rubidium was incredibly accurate but even that became redundant years later when things like cell phone systems required an even greater degree of exactness.
I was most interested to see on Benjay’s Google+ page, he made use of items such as his daughters shape boxes to house amplifiers, speakers etc. It’s alway been a challenge to find non-expensive cases and cabinets for one’s projects and I think Benjay’s solutions are pretty innovative. I’ll work back to that but I have to start the story differently.
When I worked in the Broadcasting industry in the 1960s and 70s, a lot of the programs we packaged for broadcast were still recorded on large, 12″, gramophone records. We even used to receive the ‘Goon Show’ by mail from the BBC on 12″ records. Tape recorders had been around for quite a few years but if you wanted a truly high quality recording, it was still done on disc. When the SABC wanted to broadcast a symphony concert from the city hall or wherever, a truck would be used to transfer the massive Neumann cutting lathe down to the venue. The machine would have to be manhandled into the building by two strong young technicians and set up with spirit levels to be truly horizontal on a solid base. A virgin wax disc was placed on the turntable and the concert would be cut on that. This precision, German-built Neumann record-cutting lathe was a really solid piece of equipment and the recordings it made were of a very high standard. For instance, the cutting head was not mounted on a swinging arm as we see with domestic record players. With a swinging arm, the cutting stylus would only run exactly true to the direction of the track at one point in its tracking arc. At all other angles of rotation, the cutting tip would be at a slight angle to the track and this would cause distortion. Later on, Hi-Fi record players in the studio and at home minimized this error by using the longest possible tone arm so that the total arc transcribed by the stylus was as flat as possible. But in the cutting lathe, no error at all was allowed and this was achieved by using a headstock that advanced the very solid and precise cutting head across the disc from edge to centre in a straight line as the recording took place.
The delicate recording on the wax disc was then taken back to a laboratory where it was electroplated with a nickel alloy in a complex multi-stage process. When the nickel plating layer was then removed from the wax original, it was an accurate and hard, negative copy of the original. This could then be used as the die for stamping out playable records. In the days before Vinyl records, the old commercial 78 speed discs were made of shellac, and if you dropped them they smashed into pieces much as a teacup would do today if you dropped it. But the records made specifically for high quality broadcasting of recordings such as the concert we have been talking about were pressed into shellac which was just the skin on an aluminium base disc. This made them more robust than commercial discs but of course they were still vulnerable and quickly developed surface noise etc. with usage. They were however only ever played a few times for broadcast purposes after which they were either archived or simply discarded.
Now this is where my story started. The shellac covered aluminium discs that were not archived were simply tossed out and we who worked in the technical department got to take boxes of them home with us for free. We would chuck such a disc into a basin of boiling water and this would cause the aluminium inside to expand and simply burst the shellac off it. We were left with a beautiful shiny aluminium disc you could see your face in, and this we could use for making equipment chassis, faceplates etc. How marvelous that was to those of us who wanted to build, amplifiers and radios and other gadgets. We would build those valve amplifiers etc. with great care so that they looked really good, The little glowing bottles would all line up like well trained soldiers and the wiring under the chassis was done painstakingly and attractively. Sometimes they looked so good that we used them just like that so everybody could see how neatly we had worked, but there were high voltages running round in those valve circuits and for this and other reasons we sometimes wanted to build our creations into outer boxes. This was however one of the trickiest tasks and we were always looking for readymade stuff to house things in just as Benjay does when he mounts his “Zinky Smokey amp and Takamine acoustic preamps” in his daughter’s old shapes boxes.
But I have become lazy in my old age and these days if I need to knock up a device for some purpose, I don’t go to so much trouble. This electronic metronome I built recently using a 555 timer chip for instance was simply installed in a plastic lunch box. I’ll do another blog on the detail of building that thing but for now, here’s just a picture to show what it looks like. Nearly every part of it came from my spares box or from the kitchen cupboard.