Hi Eddie,
Everything you ever wanted to know about the Minimod is in this thread
https://www.vintage-radio.net/forum/...d.php?t=149604
Including the original article from the BVWS Bulletin. There is a circuit diagram shown in post #4.
Luckily I didn't know there might be instability with the LM386, so I have not had the least problem with it!!
I've built three MM's, the first on a tiny piece of Veroboard with no thought for the layout, the other two on PCB's. They have all worked perfectly.
My thought would be to try another LM386 from a different source. IC's seem very variable these days, there seems to be loads of either poor spec or just plain fakes of many components out there.
It's a great little unit: I just need to finish repairing the radio it was meant for!
Cheers
Nick