When is a lunch box not a lunch box?

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. Neumann disc-cutting lathe

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 gCompleted unit - angle shoto 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.

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Growing up with car radios

I spent a large part of my life as a technologist with a major broadcaster. But long before that I was an unruly kid who built electronic gadgets like radios and things and often caused little explosions and minor household disasters. My parents were very long suffering.

During my early years I installed quite a few car radios. 12F8 valveIn those pre-transistor days they were valve sets, and those valves needed a high DC voltage on their anodes to make them work. To achieve that we had to install a vibrator pack in the engine compartment. It made a loud clattering sound as the vibrating contact blade switched the voltage from the car battery fast between positive and negative to produce an alternating current. The voltage could then be stepped up by a transformer to 90 volts or more for the valve anodes. The high voltage then had to be reconverted to DC (continuous current) because that’s what the valves needed. The vibrator pack was bulky and noisy and interfered electrically with the radio, so all sorts of screening and silencing systems had to be used. In the end, all we could receive was a pretty ropy AM (medium-wave) radio signal. Some radios had shortwave as well but interference from the vibrator & the engine usually made that unlistenable. To buy a set of car spark-plug leads today is a pretty expensive exercise because instead of using normal wire they are made of special carbon-based composites. This allows the high voltage for the spark plugs to pass whilst at the same time preventing the leads from causing radio interference.

When FM (Frequency Modulation) came on the scene in the 60s, it was  by its nature far less sensitive to interference from electrical pulses given off by the various parts of a car engine. That’s because spark interference has the same nature as an AM (Amplitude Modulated) radio signal. The interference would mix with the radio transmission and the AM radios of the time couldn’t discriminate between the interference and the program. FM on the other hand ignores the amplitude variations of the radio carrier and detects instead variations in the incoming radio wave frequency i.e the rate at which the signal changes polarity. The frequency is varied by the transmitter in a manner that represents the music or whatever. Electrical sparks in cars don’t affect the frequency of the FM wave so, if strong enough, the program is heard without noise.

Today we are moving a step further with technology by introducing digital radio. The signal at the studio is turned into a pattern of pulses which digitally define the program signal, and the receiver knows what the code should look like. It therefore totally rejects any interference that is not digital code and the result is a perfectly clear signal. It also works much better than FM in weak reception areas. Digital transmissions are also not confused when ghost signals reach the receiver slightly delayed after reflecting off buildings or mountains.  This was a problem with earlier technologies.

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