The Racal RA63

I’m often asked if I ever have any SSB adapters. Last December (2016) I picked up a couple of adapters from a friend with a view to getting them working and then selling them on, on his behalf. This gave me the perfect opportunity to look at them in detail and understand them better. One was an RA63B, the other was a customised RA98.

As the photograph above shows, the RA63 was not in a pretty state. Two of the knobs were missing, as was the Perspex window behind the Fine Tune knob.

The story wasn’t much better on the inside. Three of the valves were missing (2 x 6AS6 and 1 x 6AU6). One of the valve cans was missing and another was the wrong height (too tall). I fitted the missing valves and powered the adapter up, carefully. No smoke … so I then connected it to my MK1 RA17. It worked … but there was a lot of noise and crackles. The audio stage, V5, 6AU6 was running VERY hot and the HT was very close to 300V … a bit high for my liking.
A peculiarity of the RA63 is that although all the valves are B7G, the screening cans are all B9A. This might be a way of minimising the build-up of heat whilst holding the valves in place … they are all mounted on their sides.
I had used my only spare 6AU6 replacing the missinge one so I ordered a couple of spares and a couple of 6X4 recifiers valves for good measure.
Whilst waiting for the new valves to arrive, I set about refurbishing the adapter.

Left: The RA63 is the simplest of all the RA17 series Sideband adapters. This is the 1st Local Oscillator … no crystal involved, just a simple L-C oscillator running at 82Khz.

Below: The 2nd Local Oscillator is a fixed-frequency L-C type running at 18KHz.

Above: The finished RA63, complete with new knobs and csutom-made replica Racal badge. Replacing the 6AU6 in the audio stage resolved the issue with noise and the HT volts dropped down to about 260V. Resolved SSB audio from the little loudspeaker is very comfortable on the ears.

RA62A For use with receivers with a 100KHz I.F
RA63B As RA63A but with North American type connectors
RA63C For use with receivers with a 465KHz I.F
RA63D Crystal controlled 1st LO at 82KHz
RA63E For use with receivers with a 455KHz I.F
RA63G Ruggedised version of RA63A
RA63H Ruggedised version of RA63B
RA63K Fully crystal controlled (1st LO is 118KHz) ... see below
RA63L Ruggedised version of RA63E

I got my hands on two more RA63s!

Spot the difference? RA63H on the left … RA63K on the right. Because the ‘K’ is fully crystal controlled, there is no ‘Fine Tune’ control. Because the 1st LO in the RA63K is 18KHz above the IF input as opposed to below the IF, the sidebands are transposed. Thus the wiring associated with Sideband switch is accordingly modified.

I thought I might spend a little time illuminating the RA63K, which is really just a ruggedised version of the RA63D. The D and K variants differ from other RA63s by being fully crystal controlled. Both the 1st and 2nd Local Oscillators utilise crystal oscillators. Unfortunately, I have not been able to find a copy of the appropriate manual, but the circuitry, in both cases, is relatively simple, so here are the schematics for the two oscillators in the RA63D & K.