Essentially, you will need to use quite a high degree of capacitance and inductance, because even the slightest ripple will still be evident. A "pi" filter (two caps with an inductor between them) will provide the best and simplest manner of filtering. The caps should be about 750 to 1000 Mfd each (max value about 1500Mfd, anything more is a diminshing return), with a working voltage of at least 180 volts. The inductor- about 1.5 to 2 henries, the exact value is not as critical as it may seem. This size of inductor will also reduce some of your output voltage due to internal resistance, as well as inductance. It will get warm.
If your isolation transformer also happens to be a variac, no problem on bringing that output voltage down to 110 volts.
You may still have some ripple, but the radio will at least be usable. Increasing the capacitance will help reduce the ripple, but you also increase the "inrush current" when the power supply is turned on- more of a risk to the inductor than anything else, but an issue if you have purchase one new.
: How do I provide 110v DC power to AK41; the isolation xformer I am using has a DC output but unfiltered and all I get is hum. I need some combination of chokes and filter caps to clean it up.