|Racal SA535 Frequency Counter
This really is an unusual unit from Racal Electronics - makers of the highly esteemed and justly famous RA17L tube receiver.
It is a frequency counter of 1.2MHz range - but instead of using nixie tubes for its display it has 6 columns of filament lamps - 10 in each column - to illuminate the individual digits on the plastic front panel - a grand total of 60 lamps (with spares included!).
This is a solid-state unit with many circuit boards and multiple transistors and appears to date from the early 1960's. I am puzzled as to why its display technology seems anachronistic even for its time and why its range is limited, compared to other units of the time.
Recently, I was contacted by Alan Hempel, formerly of the Australian Post Office, who tells me:
" They were sold in large numbers at a cheap price to phone companies (such as the one I worked for), where the 0 to 1.2 MHz coverage was ideal for maintaining the multichannel carrier telephone gear that was common in the 1960's. These Racal counters have a pulse-length/timing feature and input stage configuration that made them ideal for working on relay based equipment too - relay circuits being used in vast quantities in 1960's telephone exchanges. I'm sure that they were designed with phone companies in mind. Unfortunately they had a high failure rate and soon got scrapped.
had a high failure rate, transistors shorted C-E being very frequent. I
remember one of my earliest jobs being given several to fix, and the
Senior Tech said to me something like "Don't waste time trying to be
clever - just identify the correct board(s) and check all the
transistors on it/them for shorts C-E. He was right, and I
replaced lots of them. Strangely, I don't recall the display lamps
failing much. They also had a unique double thickness PCB for the
power supply, adding
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Last updated 30th March 2013