[Nick3092]

Nick,

if your other pot that gave you volume no longer works, it is then posibly not the pot, unless the other pot is bad also.

First test: disconnect the pot fully, connect the 1st Audio input (cap 101) that went to the pot's wiper to the 2nd Det output (cap 74) that went to the pot's top pin.
That should give you full unattenuated volume.

See if this works.

PS. I am not sure why it should be positive on the grids. From the sch it should be negative to the chassis. Grids are pulled to the B-, and cathodes to Chassis, and chassis is above the B-, so Cathodes (filaments) have to be negative .

I'm pretty confident both pots are working correctly, based on using them to feem the signal tracer.  They woirk as expected.

Connecting the two caps together just gives me a whole lot of crackles and pops.  Something else is wrong in the audio stage causing the 1st audio 6J5 to have double the plate voltage.