Time to call in an experienced electrician to check the power connections at the panel box, outlets and from the street service. I doubt it is an equipment problem.
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Are your IC's close to any power cables, especially the phono amps power supply? I had a similar issue a few weeks ago. I used grey pipe insulation that you can find at any hardware store as an experiment, and wrapped the phono IC's, and it worked to eliminate the hum. I would look at wrapping anything that crosses the path of the tube phono amp's cables. You will need to experiement. Last, make sure your are using the ground wire correctly from the tonearm cable. It should be grounded to the phono amp chasis.
I assume your toneam is grounded to the preamp and you have tried it without it being grounded to see if there is a change. Do you have the ability to plug your preamp into a different outlet from the tonearm or amp? One that is on a different circuit in your house? As for RF, is your tonearm cable shielded? What about your other ICs. I have only run into that problem with unshielded cables.
good luck. let us know.
If I'm not mistaken low level hum is usually a ground issue. Is your abode a modern one or do you live in an old building? I know many old buildings do not have grounded electrical, so you need to find a true ground to tap into to overcome it. Also, all tube make noise, but this is usually not very noticeable unless the volume is up pretty high (on my Cary SLI-80 that is). Sometimes you will get a very noisy tube, however, so you might look into that. I almost bought a the Fosgate that you have until my local dealer told me that they are rather tricky to match the tubes to the desired sound. He did not mention hum or tube noise, only that this amp is pretty finicky and that tube rolling is part of owning one. I'm not sure what to tell you about RF. I get it as well but only through my phono section so I think it is the cartridge that picks it up, and it is not audible when playing music.
I would have your local dealer try to help you isolate the source of the hum. One usual suspect is the cabling. Are your ICs shielded? If you have no luck with your dealer, then definitely follow up with VPI and Fosgate customer service to see if they can help you pinpoint the source of the humm. My guess is they go through this a lot and are pretty good at diagnosing the source. Good luck.
You have probably though of this already but you may have a gain mismatch between you cart and you phonopre. If you have other tubes, I would try them to rule out that yours may be bad. Also, I doubt this is your problem, but I had some noise issues and was able to take care of it with cables. When I used a very well shielded cable like Audioquest, it took care of the noise. Please understand, I hate recommending cables and urge you to try cables first and not buy them unless you are sure they fix the problem.
In a single-ended system, there are many sources of hum. Tubes per se are usually NOT one of them. You probably have a ground loop somewhere. Try ungrounding some of the items that are now grounded. You don't tell us much about that. Have you grounded your tonearm? Your turntable? Etc. Have you tried bypassing the Running Springs (never heard of it, but great marketing name)? Above all, I would advise you not to buy another piece of gear to cure this problem, because you have zero idea of the cause and it would be a complete shot in the dark. As to RF; what are you hearing that makes you think you have RF problems?
Typically if the noise increases with volume a component is the problem. However, there are easy but time consuming ways to diagnose the problem. It would help if you had a set of shorting plugs handy for the diagnostics. Maybe even a set of Jensen plugs used specifically to detect ground loops. Cheater plugs are also something you should have on hand.
In any case remove everything from your system but the amp and speakers. This means removing all appropriate interconnects and power cables. My recommendation would be to plug your amp into a wall socket, not the Running Springs. Short the inputs of your amp and turn it on. Listen for hum and noise. If you hear noise it could be the problem or just one piece of it. Try a cheater plug on the power cable and see if the noise goes away. Continue hooking up each component one at a time repeating the exercise.
The Ground Zero never worked for me and is more pain than pleasure IMO. Running Springs makes great products but don't rule it out as part of the problem. I typically have only one component grounded in my system and float the grounds on the others. This may or may not work for you. Also, is your equipment single ended, balanced or a combination of both?
Lewm.... I have the VPI turntable grounded to the Fosgate phono preamp. All the equipment power cords are grounded, but you have a good idea for me to unground these, one at a time. I'll try that. I also agree with about buying another piece of equipment without knowing what's going on first. Thank you, I'll report back after I try ungrounding the pc's.
Manutius....The tone arm cable (in the VPI tonearm) is nordost . I'm using Purist Venustas IC's from the tonearm to the Fosgate. However, I an using unshielded IC's (Speltz phono cable) from the phono preamble to the preamble. I have already changed that pair of IC's to a shielded pair, but that made no difference.