RA117 serial number N0489 (/cont)

No surprises with the Calibrator … the design of this little enigmatic box has remained more or less unchanged since it’s inception.


It is also very easy to work on. It is often much maligned though as a ‘pig’ of a circuit to get working. I’m no magician, but I have re-built at least eight calibrators to date and never once have I encountered a problem. Admittedly the user-manual is a tad vague.


Here is how I do it:

Obviously you need a working receiver. With the System switch set to ‘Cal’ tune the KHz dial to a multiple of 100. 500 is a good starting point. Now adjust L69/70 (the one furthest from VFO2) for an increase in noise or even a tone!. If L75 is not properly set you are more likely to get noise rather than tone initially. Now adjust L75. Generally you will hear a further increase in noise and then possibly a spontaneous tone. It may be necessary to adjust the KHz setting too. If you don’t get a tone it is likely that you have tuned one of the cores to a ‘false’ response. In which case you just need to find the correct one by re-tuning either of the two cores. Once you have a tone, verify that it is present every 100KHz from 0 to 1000. It not, it is simply a matter of carefully tweaking either of the two cores again (most likely L75) and verifying the response over the range. It isn’t a ‘black art’. I think it is just something that you get a feel for.