Thanks Whirlwind and Parbaked. You are right. I remember Mr. Peppard telling me that only the driver tubes makes a difference. I do not know much about tubes, and will have to do some research. But as far as I know, there are very many 5751 tubes out there, which makes it very difficult to know which one to get and where to buy. Specific suggestions to improve on the stock driver tube? And do you know a reliable seller to get two new 12B4A tubes?