[Tgace459]

If B+ is there then yes, you're right, the filaments are fine.
I would disregard the light for now and concentrate on sound.

He had Plate voltage on 50L6 so his output xfmr is likely good.

Need to check the speaker.

Try to touch pin5 pf 50L6 with a screwdriver (be careful, high voltages around, use one hand only and stand on an insulating mat if in basement), see if you have hum.
If not,
Disconnect the speaker from xfmr secondary and measure across the speaker with ohmmeter. Should be almost short, 0.45 ohm.

I'm powered down now and cleaning pins and sockets...but assuming I'm testing from the right points, which are the two terminals on the speaker that have push-on connectors to the transformer, the speaker is testing at 3 ohms.

I can get sound from the speaker if I jump the 2 points with a 9 volt....