[Chas]

Thinking of lowering the grid resistor values.

I should not have mentioned that But I will repeat, that is done only when the radio is used in a remote location. If the procedure is done it may obscure other problems or make them worse. Keep the value at 600 ohms for now.

Look around the Atwater-Kent web site. I believe there are many model handbooks reproduced that explain how to set up the radio, antenna, ground, batteries and speaker.

Begin with a triage, take ohmmeter (I highly recommend the use of an analog meter) readings of all the connections, but plan on re-soldering all of them. Be sure the rheostats are working and not worn or burned out.

Be sure all the tube pins are cleaned.

Determine exactly what is to be done about the audio transformers...
A-K recommends the use of NuJol a pharmaceutical mineral oil to lubricate any moving parts. If the rheostat compartment is opened petroleum jelly is used to lube the slider and finger contact.

The "A" or filament circuit is critical in respect that getting a crossed connection to B+ will destroy the tubes.

This may help:

https://www.arborsci.com/blogs/cool/thre...omagnetism

However, the only need is to see which way the diaphragm pulls in or out with the polarity. Tracers on wires are for identification for the layman who would not have an ohmmeter.

If this radio uses a battery cable be aware that the color coding will have faded. Confirm where all the cable wires are going. Re-color the wires with a Sharpie or make tape flags with the proper identifications. The ends of the wires can be cleaned up and tinned, a little sealant applied to keep the textile from fraying.

Chas