The question, ‘What defines an RA17 MK2 from a MK1?’ is a common one and anyone could be forgiven for thinking that there must be precise delineating features. However, the more I look into the issue, the more muddy the waters become. BUT, before I go any further and it is pointed out by someone else, some RA17 MK2s do actually state MK2 on the serial number plate as in the picture below. It wasn’t always like that though …

There is even a school of thought that marks the boundary between RA17 and RA17 MK2 thus: ‘those with serial numbers 511 and above are MK2s’. This premise is probably based on the annotation at the bottom of the circuit diagram in early RA17 manuals. See the picture below.

But that ‘argument’ doesn’t hold much water either. A few years ago I was given the remains of RA17 Ser. N573. It was missing the VFO-1 module and the calibrator. Through time I obtained replacements for these and eventually proceeded to rebuild the receiver, and it didn’t take me long to realise that something was different about the power supply. There was no 9K ‘stand-by’ resistor, yet there was a ‘STAND  BY’ position on the front panel switch. What was perplexing was the fact that although the switch had 5 positions, there were only 5 solder-tags per wafer. This implied, and I verified the fact, that when the switch was in the ‘stand by’ position the wiper was in effect ‘pointing’ to itself!. See the image below, taken from an early Racal brochure for the RA17. I don’t have a photograph of N573’s PSU but this is what it looked like. Note the missing resistor. Then compare it with the photograph next to it of an other early RA17, this time with the 9K resistor.

Thus, you would think that here is clear evidence of where a MK2 differs from what we will call a MK1. But you would be wrong because the photograph on the right is in fact from RA17 N558 and obviously pre-dates N573

Is your RA17 a MK1 or MK2?