[allan]

I solved my local oscillator (6K8) problem. Looking at the medium wave performance, I could see a reasonable sine wave over half the dial but it cut out abruptly at 1.5MHz when it should have gone up to around 2MHz.
I changed all the capacitors, increased the HT, swapped some resistors and finally heated the coil with a hairdrier. The amplitude increased from 8 volts to around 12 volts. It then started to drop. Removing the heat left the amplitude at about 12 volts but still cutting out at a little over 1.5MHz.
I then abandoned MW and looked at LW which was completely dead and found the coil feedback winding was open circuit. I fixed this and then looked at the MW coil. It also had an open circuit feedback coil. I fixed this and refitted both coils.
As I turned up the HT towards 250 volts I saw the LW oscillator start up at only 30 odd volts of HT. It rose to over 15 volts RMS and only dropped to 13 volts at the other extreme of the band.
MW also started up at 30 volts HT with the amplitude ranging from 11 to 16 volts at 250 volts HT.
Interestingly the MW coil feedback winding measured 66 ohms so may use a type of resistance wire to tame oscillations.

The AR88 uses tapped coils with capacitor potentiometers and not a feedback winding so will have a different fault... eg. a poor wavechange switch wiper?
Allan