[Phlogiston]

Never seen a 6BE6 as an AM RF amp. Those are usually heptodes like 6BA6/6AU6/6BJ6. 6BE6 is a pentagrid converter, used as oscillator/1st detector stage for AM. I've seen them used for FM as well. Not all that good at it, but they do work with clever engineering.

Yes - exactly. The converter tube for AM was powering up -down. The voltage change this was causing (mostly a small change in fil voltage) was messing up my FM sweep(s).