Wurlitzer 2500 MONO amplifier issue?

Good Day

I do have a 1961 WURLITZER 2500, Serial NB 494016.

Last week, while playing, the sound stopped suddently, while everything else was working ok.

Upon opening the glass, I could lightly smell kind of electric component fumes, but not persistant.

If played again, the speakers hummed constantly.

I checked inside the amplifier rack. The 5 tubes seemed to be working (all the heating filaments slightly glowing)

All fuses are OK.

Any help please? Thank you!!!