Elizabeth, I have kept both my Audible Illusions Modulus 3 and Modulus 3A four tube preamp on continuiously since I bought them. The Modulus 3 has been on constantly for 16 years and the Modulus 3A for 10 years. The only time I have turned them off is when I changed tubes. There is no danger keeping a modern tube preamp on all the time.
Bob
Bob