Hi Ralphww: There are really no "stock" tubes that come with the Mercury preamps. It's my understanding that Kara et al matches tubes in pairs regardless of the brand. I personally have ALL Sylvania tubes running right now that I bought from Andy at Vintage Tube Services. Also, I found that if you replace the 5AW4 rectifier tube with a 5U4GB, it really tightness up your sound. Good listening. Jeff
