Hello,
I have recently build my first headphone amp, the Bottlehead crack. I tremedously enjoyed it, everything worked right away, all parts were there, and it sounds fantastic.
I inlcuded a step attenuator from the beginning, and later the Speedball upgrade. Then I added some film caps, the choke, and the Cree diodes. I am using an input tube from Tube Amp Doctor (12AU7WA / E82CC TAD Premium Selected). This together with the stock power tube sounds incredibly nice. I tried an inexpensive Chinese tube (6AS7G / 6N5P Shuguang, see picture below), but that didn't sound good. So I wanted to see what all the fuss is about the Tung Sol 5998, despite the high price.
Yesterday, the tube was delivered from a seller with spottless reputation, and I had some time to listen to it before leaving for a trip. It is indeed more detailed and stages better, right in the first minutes of use. But I realized that if you carefully tap the tube with the fingernail you hear some 'tink' sound. The tube seems to be perfectly quite while playing music.
My questions are: Is this a microphonic tube? Would you be ok with using this one if it does not make noises while playing music. I found very different opinions about if this is a problem with microphony or inavoidable. Also, some people expect microphony from the input tubes, but not from output tubes. Some say, tapping a hot tube with the fingernail might even harm the tube.
I would appreciate some advice. I am very new to DIY tube gear, and I have payed almost $200 for this tube and want to make sure that it is a solid investment.
Thank you!