I think your KW500 uses 6SL7s in the preamp section. These tubes have high gain and are not as quiet. Do follow the suggestion of swapping tubes from side to side. If the noises follow the swapping, then it is quite obvious.
If the noises are indeed from a bad tube, order some tubes from a reputable dealer. Some people here stated that they had good experiences with upscale aduio. With 6SL7s, I would order platinum grade to get lower noises.
Hope it helps.
If the noises are indeed from a bad tube, order some tubes from a reputable dealer. Some people here stated that they had good experiences with upscale aduio. With 6SL7s, I would order platinum grade to get lower noises.
Hope it helps.