[R-390] R390A- Intermittent sensitivity variation

[Eric Gauja]

Hi Group,
                  I have mentioned in previous posts (Greetings from Sydney, Australia) that I have noticed variation in calibration signal levels with my 1963 Imperial R390A.  After a longer period of investigation, I note that the problem is actually confined to the 16 –32 MHz octave. On any one of the 16 –31 MHz segments ,  a calibration signal level of say 20dB as read on the carrier level meter can suddenly shift downwards to 10 dB or lower.  The problem is not in the calibration signal, because  if I switch back to a signal off the antenna, it has also dropped in level.   This shift in sensitivity is intermittent – it does not coincide with warm up after switch on , but can occur at any time – another observation is that sometimes sensitivity can be restored by moving the MCs knob a few notches – but not always- sometimes the sensitivity restores by itself after an unpredictable period.   I am quite new to the group, but have been studying the Y2K manual , and the wealth of information on the R390A FAQ page, as well as past posts to the group, but have not yet seen any specific mention of my problem.  Since the sensitivity variation is confined to the 16- 32 MHz range, I suspect a problem with the RF deck 16-32MHz circuitry. Could it be a problem with the bandswitch contacts in the 16-32MHz section or could it be a problem with the coils and/or capacitors in this section?   Any advice from the group would be most appreciated.   There are no problems with sensitivity variation below 16 MHz.

Best Regards to all,
                                     Eric.