After acquiring a vintage ham radio transmitter for use as a pirate radio transmitter (or any other use), it is advisable to replace any of the old paper or electrolytic capacitors with new ones. The same updating should be done to vintage receivers or television sets. These types of capacitors age and fail over time, and replacing them may be necessary for safety reasons, beyond getting your radio to work correctly.
This article, while intended for those restoring vintage radios and televisions, applies equally to restoring aging ham radio transmitters such as the Johnson Vikings, Valiants and Rangers, Heathkits, Collins, etc., or any other tube transmitters manufactured from the 1930s through the 1970s. It is written for the "beginner" in radio restoration, and goes through the types of capacitors to be replaced, what they look like, and how to do it. (I would have found it very helpful and time-saving to have had all this information in one place back when I was doing transmitter restorations.)
Click here: http://antiqueradio.org/recap.htm