Racal SA.540 Universal Counter Timer

[factory]

I recently added a rather uncommon Racal SA.540 universal counter timer to my collection of vintage test gear, it's fully transistorised counter that is good for up to 11MHz or 100MHz with the optional SA.550 range extension unit (I missed one of those a couple of months ago as I didn't know what it was for at the time), the combined setup of the SA.540 & SA.550 is also known as the CT488.

It dates from the mid 60's, there is an advert in the May 1966 Wireless World (see page 10 of the pdf); https://worldradiohistory.com/UK/Wir...ld-1966-05.pdf

I had to trace out the mains wiring to make up a power lead as it uses the Plessey type connector, amazingly it seems to be mostly working (as expected a few of the lamps are blown, but I have plenty of spares), I used the HP 4204A to test the display lamps.



Inside the top section has a few spare lamps, as previously mentioned on the forum the circuit boards for this era of Racal counter are all soldered in making servicing rather tricky.



David

[Julesomega]

Another one in a series of these Racal counters with columns of illuminated numbers. This seems to be a development of the Racal SA535B which in turn was one of the successors to the Digital Frequency Meter SA-520. That page will give you a link to the Numitron version, the SA-520B

I expect the 100MHz prescaler uses a 'ring of ten' counter, a sort of deca-stable which I have seen in an earlier Racal counter, the 801M, for which I hope one day to find some service information

[trh01uk]

Julian,

if you want the technical manual for the 801M its apparently on the mods.dk site under the Racal section. I can't check as I have exceeded my download limit!

Richard

[factory]

Originally Posted by Julesomega

Another one in a series of these Racal counters with columns of illuminated numbers. This seems to be a development of the Racal SA535B which in turn was one of the successors to the Digital Frequency Meter SA-520. That page will give you a link to the Numitron version, the SA-520B

I expect the 100MHz prescaler uses a 'ring of ten' counter, a sort of deca-stable which I have seen in an earlier Racal counter, the 801M, for which I hope one day to find some service information

I do have the column display version of the SA.520, it's quite a lot smaller & lighter than the SA.540.
They would have sold a range of these counters at the same time with increased/different functionality & amount of digits. Not all of the customers would have wanted/needed the most expensive version or functions they didn't need.

Here is a saved picture from eBay showing the inside of a 801M, it does look a fair bit newer than the SA.540 counter I have here.

I think another magazine described the SA.550 pre-scaler as having a tunnel diode based circuit, I need to find the article again as I didn't save a link.

David

[factory]

Some pictures of the SA.550/CT488 pre-scaler that sold recently, which I should have bid on (but didn't as I had no idea it was for this counter), I hope it didn't get scrapped.


Removing the bottom panel from the SA.540 it has the matching connector underneath, the panel looks to fit the bottom of the SA.550 but I'm not sure about whether it had some extra side panels or needed a complete replacement top cover.

David