05-22-2013, 08:16 AM
The 6A5G is a 6B4G with indirectly heated cathodes, It looks just like a 6A3 or 6B4G, but if you look carefully there are tiny cathode sleeves placed over each filament. The 6A5G was designed to eliminate the hum caused by heating the filament with AC. There is a separate pin for the cathode connection which is also connected internally to the filament center tap.
http://www.bunkerofdoom.com/tubes/syl43/...9/6A5G.GIF
http://www.bunkerofdoom.com/tubes/syl43/...9/6A5G.GIF