"Re capping " means to replace the old capacitors with new ones.
The main reason for this is that the manufacturing abilities back when these old radios were new was not able at that time to make long-life reliable capacitors as they do now.
There are three basic types.
1.)Wet or dry Aluminum Electrolytic - Typical values are 5uf-100uf @ 150-450vDC, used for large values especially those needed in the power supply filter section.
2.) Aluminum foil & Paper with wax coating - typical values from .001uf to .1uf @ 400-630vdc
3.) silver & mica in a plastic case - Typical values are 5pf- 1000pf @ 500-1000vdc
Types 1 and 2 both age poorly and will definitely need to be replaced in any of these old radios made in the 30-50s
The problem is that as they age they become leaky and act as a resistor drawing excess current and wreaking havoc in the circuit.
Type 3 is rarely found to be bad but after 70 years or so now these too are beginning to show increased failures.
Especially if the component has a brand name on it "Micamold" or if the value is greater than .001uf.. Replace it.
Resistors also drift high with age and if found to be of more than 20% of the stated value should also be replaced.
All these parts can be purchased from:http://www.justradios.com