A few words for those now getting around to tube rolling in their Gk-1's, specifically with the 7308 tube. Tube rolling is part of the hobby and easy to do. There's a lot of info on this in older threads, and no need to repeat any of it. Most people's experiences with these tubes in the GK-1 is similar, as we all have nearly the same amp as well.
I continue to see 2/3 words repeated over and over, these being Siemens and Gold pin. The 7308 was a premium specification of the 6dj8 tube and was developed by Amperex in the 60's. Siemens was a later manufacturer, and continued to make these tubes into the 80's. Read any of the NOS tube sites, all pretty much agree that Amperex tubes are the best.
Gold pins have nothing to do with Siemens. Gold pins are a specification of the 7308 tube. ALL 7308's have gold pins, no matter who made them. If the tube does NOT have gold pins and pretends to be a 7308, it's a fake.
The main reason the 7308 tubes are so expensive is simple supply and demand, as in low supply and high demand. Andy Bowman told me that for each flat of a hundred or so of these tubes he gets, he's lucky to get one or two that actually work. Most are no good and he just throws them away. I got a pair of 1964 Amperex's from him a couple years ago for 65 USD each. Andy does not gouge!
He also will usually have some very good 7308's made by Matushita in Japan, for about 35 USD each I believe. He talks up the Japanese tubes pretty good. For the GK-1 application, these Japanese tubes might be the best way to go. Most of the best qualities of the 7308 are just not needed in the GK-1 design. Ask Hugh. He's explained it elsewhere.
Andy Bowman is at
www.vintagetubeservices.com, and likes to do business by phone.
Another possibility for the GK-1 is finding some NOS 6es8 tubes. I don't know if these NOS tubes would perform any better than the inexpensive stock tube, but the GK-1 is designed for the 6es8 tube. NOS 6es8's are not plentiful, but they can be found.
