If you're going to do it correctly, rebuilt the amplifier. New capacitors and tubes are a must. Remember, this amplifier is pushing 50 years old. If you're not comfortable rebuilding an amplifier, send it to Jukebox Friday Night. When you get it back, it's like the day it rolled off the factory floor.
Using any vintage amplifier with old capacitors and tubes may present a short to the output transformers, causing burnout. These transformers can not be replaced. They don't exist.
Is your amp cover missing? Originally, this was a piece of 1/4" plywood. It protects the records from tube heat. Very important! You can replace this wood cover with a piece of clear 1/4" plexiglass. It serves the purpose and allows visibility.
Without a tube tester, don't chance old tubes. Buy new ones. Good, used is not recommended. Buy new, or NOS. Do not substitute tube designation numbers. Your tubes are 100% of your audio. Make it sound great.
It has been said that the solder lugs have been known to turn and short, taking out the audio transformers. It is suggested that you either tighten these lugs very well, or remove them. Tubes aren't cheap, but tranformers are cost prohibitive, if they are even available. Your Princess does not provide cabinet stereo. You must have external speakers to achieve stereo sound. The cabinet speaker is a mono mix.