Hi Nick72. I swappped out the 5AW4 for a 5U4GB in my Mercury, and there was a great improvement. The sound tightened up very noticeably. I use all Sylvania tubes right now, but would like to try some other brands. I buy my tubes from Andy at Vintage Tube Services (616-454-3467) whenever I can. He can answer ANY questions you have regarding tubes. I bought the 5U4GB on Ebay for $15 total.
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