Check tube sockets! The GTA SE-40 did not have the best tube sockets. With the amp cold, take out the tubes for the channel making the noise one by one and reinsert, as to not change the placement or order of the tubes.
Frequently it's the 6SN7GT input tubes that are the culprits. Sometimes tubes will "walk" slightly within the sockets as they heat up and expand, then cool and contract.
-David
Frequently it's the 6SN7GT input tubes that are the culprits. Sometimes tubes will "walk" slightly within the sockets as they heat up and expand, then cool and contract.
-David