Sometime back I compared RCA blackplate 5751s, the EH 12ax7s, and EH goldpin 5751s. I preferred the EH goldpin 5751s to everything (there were many others) except Telefunken 12ax7 smoothplates. For less than 40 bucks I strongly recommend trying EH 5751s. But.... the keyword is "trying." What worked for me and my system may not for you!
