- Jan 22, 2008
I believe it would be a sign of a defective tube (grid current?). Or wrong implementation (capacitive coupling?).I read somewhere that in tube stages much larger foil caps can sometimes be used to good effect with regards noise . The idea was that by making the cut off frequency of the filter much lower , the output impedence of the preceeding valve could help reduce low frequency noise at the following valve grid.
Anyone any thoughts on this ?