Hi Marco,
Yes that's an interesting tube. I happened to find replacements for all the tubes in my collection, so I tried swopping them out as well, but it made no difference. Very satisfying stumbling on the fault eventually
I have recently built a low power am transmitter (attached) that the Philips tuner picks up around 1590kHz. Just a fun toy to play my own music. Local stations here on AM are scarce (3), and the music they play is terrible.
My next hurdle is to research FM!
All the best.
Paul