Harry,
Stay with it, your persistence will be rewarded. Here is a quote from my earlier experience; hope it helps
"I have been working on, and continue to work on reducing the hum. Whether it is a hum or a buzz may be an important distinction that I am not sure I can entirely distinguish. But this quest of noise reduction has been fruitful in moving down the noise floor.
A large reduction in noise occurred when I replaced my "economic" used tubes with NOS Telefunkens. The 12AU7 Telefunkens in the Clarinet were very quiet except for an intermittent ring. The ring was not volume dependent or input dependent. So it was evident that the ring came from the Clarinet. Tubesforever wrote that he experienced similar ringing that was solved by tube selection. So I tried swapping the tube positions and the ringing went away.
The Cornet2 is now the major focus of noise reduction. I have noticed that when I place my hand on the transformer, the Cornet TX is hotter then the Clarinet's. There is one more tube in the Cornet than the Clarinet so this may be the reason. But, I have a notion that heat is equated with noise (entropy). The first stage tube in the Cornet may be the most critical position for a low noise tube. Isn't this a reoccurring theme throughout the archives of this chat site? I've tried a GE, Mullard, Amperex Bugle Boy, and Telefunken 12AX7 tube in this critical spot and the the Telefunken is clearly the lowest noise winner in my system. Unfortunately, the Telefunken is also the most expensive. However, apart from the noise, each tube has interesting sound characteristics that could appeal to different tastes. The GE was used, noisy and used for component burn-in so its sound was not expected, nor performed to the standard of the others. The Bugle Boy added a liveliness to the music that is fun and beyond the laid back sound of the Mullard and Telefunken. I would likely be happy with the Bugle Boy if I could find one (they seem to be harder to find) with lower noise. The Mullard has a full, well behaved, maybe even lush sound that is pleasant that I would also be happy with if the Telefunken was not so quiet. But because the Telefunken is so quiet with a reputation of having a long life with little drift, this is my choice (today).
The laying of hands was an interesting experience. When I placed one hand on the Clarinet transformer, I could move my other hand over various components and places around my system to induce noise. I took this as a way to identify what items may benefit from further modification. I did a similar test with the non-shielded interconnects as written previously. When the noise increased when my hand or the cable was in close proximity to any item, that item was suspect. The shielding of the interconnects was very important in my system. These shields are connected only to the source ground lug. When I lift these connections a definite rise in hum occurs, so I am encouraged that something good is accomplished. In terms of the most critical interconnect, it seems to be the IC between the SUT and the Cornet2. The SUT can be quite noisy if not properly grounded. I have tried to examine my grounding system to determine where the center of the star grounding is. It appears to be the shield of the Cardas tone arm cable from the turntable at the SUT input. This arrangement provides my system the lowest noise floor so far (but is subject to further testing) and creates the largest hum when disconnected."
ronpod
