Lightning and other mishaps
Written by Bryce Ringwood   

About a year or so ago, I was presented with a Philips transistor radio that according to the owner had been struck by lightning. Fortunately, Old Lightning Arrester Advertthe lightning strike must have been quite some distance away, otherwise it would have been unrepairable. As luck would have it, I had replacement transistors to hand, and the worst damage was confined to the circuits in the “front end”. What was remarkable, was the fact that some of the tracks on the printed circuit board had been burned clear away, leaving a ghostly impression on the printed circuit substrate. These tracks were replaced with fine wire and a few dabs of superglue to hold everything in place and the set duly came back to life.

Aerials, by their nature attract lightning strikes. The most prevalent form of protection seems to be a “spark-gap” - simply two points of wire spaced a small distance apart so that any high voltage will jump the gap and not damage the equipment. Probably almost equally useless is my own favourite, the “gas arrestor” connected across the aerial and earth. Whilst they may be marginally effective with valve radios, they are probably totally ineffective for solid-state (i.e. transistor) circuits.

It has been a family tradition to disconnect the aerial from TVs, radios etc. While there are storms about and before going away on holiday. Last Summer, I was using a Kenwood R1000 and there was a distant rumbling. The next moment a 25 cm spark jumped from the case of the set to my finger. Amazingly both finger and radio were unscathed, but it did bring to mind how careful one has to be.

I was less lucky when ESKOM decided that if 230 volts was good, then 320 volts would be even better. This took out a printer transformer and a transformer for one of my radios (fortunately switched off!). I reported the problem to no avail and wrote the transformers off to experience.. At least, this sort of problem can be averted by purchasing a constant voltage transformer.

Call me paranoid, but unless I'm present, I unplug all my radios and disconnect them from the mains.



 
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