Re: Building the 'Minimod' AM modulator-questions!
Mike, it seems weird that nobody else has noticed any frequency drift although it is possible that nobody else has used one with a 'modern' set with frequency synthesis tuning!
Are you sure that there isn't a change in room temperature during the same period that you've noticed the drifting - in which case the temperature coefficient of C1 might be responsible.
Apart from that, the FET could be responsible - I certainly don't think you moving core theory is responsible - but, if the core is noticeably loose in the former, why not add a piece of elastic, a very narrow strip of PTFE tape or just some core locking compound, if you have any?
Oops! Just spotted in post #31 that you've already eliminated C1 as the cause
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