Re: Chapman radio
There may be a significant amount of residual IF getting into the output stage and being radiated- it's not unusual in the typical two-stage AF amplifier stage in radios like this (I assume that the ECL86 is being used in this fashion) for there to be a capacitor in the low hundreds of pF between the 1st AF stage anode and ground to filter IF that has got through this stage out of the subsequent AF output stage. Sometimes, there's also a stopper of perhaps 10-22k in series with the AF output stage control grid.
Apologies if you've already been through this!
|