Hey I have 2 Art Pro MPA's just like you and I had read your post a long time ago about how you swapped out the tubes. I have tried to locate either some westinghouse 12df7 or raytheon 12df7's but to no avail. Any other suggestions as to what kind of tubes I could try. I'm looking for one with possible a warm sound and kind of on the darker side. Thanks for your help.