[RodB]

When you consider electrolytic caps in power supply filters there's a wide tolerance except for the first one at the cathode. For that one it's best to match as close as possible so you don't damage the rectifier. Most tube manuals will have the maximum input filter capacity listed for power rectifiers. You're right about the 22mfd, I find it cheaper to order a quantity of ten and get the price break. I probably use 47 and 22 more than any other values.