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Mike. Watterson · 21st Apr 2019, 11:58 am

Did you replace the discriminator capacitor? Usually about 4uF, 25V to 50V and POSITIVE to chassis/OV!

If not, then the discriminator coil may have been tweaked. Easy to sort with a wobbulator, otherwise use 10.7 MHz signal generator. Normally carrier off, but later you can turn on AM to see rejection.
The centre of the 10.7MHz needs to be at the middle of the slope of one side of the discriminator coil, not at the peak. If that's been peaked at 10.7MHz, then you have to tune off centre on the IF and creates distortion.

Great you've made good progress.

21st Apr 2019, 11:58 am	#129
Mike. Watterson Heptode Join Date: Dec 2014 Location: Limerick, Ireland. Posts: 901	Re: Ferguson 382U Firefly not playing ball Did you replace the discriminator capacitor? Usually about 4uF, 25V to 50V and POSITIVE to chassis/OV! If not, then the discriminator coil may have been tweaked. Easy to sort with a wobbulator, otherwise use 10.7 MHz signal generator. Normally carrier off, but later you can turn on AM to see rejection. The centre of the 10.7MHz needs to be at the middle of the slope of one side of the discriminator coil, not at the peak. If that's been peaked at 10.7MHz, then you have to tune off centre on the IF and creates distortion. Great you've made good progress.