The design of your tube amplifier is the use of 6SN7,6SL7,ECC32,ECC33,ECC35,5691,6592,B65,6N8P or CV181.
If you want to try 6CG7. Only need to connect 6CG7 and the adapter socket in together.
Then connect to your amplifier,begin to enjoy music.
Needn't change anything about your amplifier.