[Chas]

In this design the AF circuits are supporting a certain amount of hum. That is negated with the hum bucking coil. Adding the additional capacitance as I suggested should abate the hum that would be present in a speaker designed without a hum bucking coil. Overall, removing the hum from the B+ removes a useless work load from the AF as a system.

Be aware adding additional capacitance to the 1st electrolytic from the rectifier is limited to the rectifier itself and any voltage increase that will occur.

You will need to find an output transformer. I would suggest a Hammond, a bit pricey but the modern design will be helpful. Be sure the output tubes are correct and in good condition, no substitutions.

GL

Chas