[morzh]

Hey Terry, thanks, I have this one and I thought there might be some "in-depth" procedure with explanations outside the Rider.

Specifically the motorboating bothers me though it only occurs for 1 sec during warmup.
Still, its presence is a testament to my ineptitude and so I, being my own harshest critic, keep calling myself names due to that.

Usually it is due to inadequate decoupling in multistage schematics, that allows radio and audio stages couple, as I remember from transistor radios, or leaky AC-coupling caps, or too high a value for grid leak resistors, but the radio is fully recapped and reresistorised.
Have to think.