RA117 serial number N0489 (/cont)

The BFO: What was an EF91 in the RA17 and 17L and a 6AU6 in the RA17C12 is now a 6AK5W in the RA117 … the basic circuit is essentially the same but with the addition of one resistor (27K) in series with g2, and it’s associated decoupling capacitor.

The next stage is to remove VFO1 and VFO2 from the chassis. At this point it is always a good idea to remove and refurbish the RF attenuator and the meter rectifier tag-board. The latter cannot be removed when VFO1 is in place and access to the four resistors and the rectifier is extremely difficult when it is in place.


Note the 1K8 resistor in the photograph on the left. This is across the input of the Low-Pass filter. I haven’t been able to find any record of this being fitted as a sanctioned mod, so I removed it.

Working on wafer switches is always tricky. The greatest risk is that the terminals get broken off when removing components. I don’t think I have even encountered a faulty resistor in one of these attenuators, however I have found one or two solder joints which had failed to the extent that the attenuation was excessive. Replacing the resistors, even though they are in spec is probably wise just the same.