Atwater Kent Model 30 Question

[polyphase]

I looked at the schematic for this set, and noted the following....

There is a cap from the 67V supply to ground. If this is the original,
it is probably leaky & should be removed. No need to replace.

The -A input is not directly grounded, but rather passes thru a fil rheostat to
ground. This means your A supply must float with respect to the other supplies.

It also ocurred to me that your A supply, if it does not include a regulator, could
be a source of hum. Even with 36000uf, at 1.5A draw, ripple would be on the order of .2Vpp a quick calculation shows. This is enough to cause trouble because the filaments are also the cathodes, and any noise here would be amplified the same as if applied to the grids.

FWIW, my preferred fil supply is a small (10Ah) 6V lead acid battery. Can be charged with a wall wart or even a solar panel.