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It just started, after about 10 years. Tube preamp and tube monoblocks; it's one monoblock that's developed the problem(s). Neither noise is loud, but it's slightly annoying. Noise #1 is constant but fades out for a second, then comes back; noise #2 is intermittent (it stop sometimes for an hour or so). Any ideas? Maybe at this age the tubes are wearing out? Or maybe it isn't the tubes at all? I don't see anything that looks abnormal, visually. They were built from kits by me.
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The high pitched whine -- almost like radio interference, bobbing in and out over two seconds or so, except it isn't radio-like in that there are no recognizable sounds. I was fooled into thinking I had solved it by replacing the input tubes as Tre' suggested, because I've since learned that the system has to have been on a while for the sound to develop.Now for the embarrassing thing: It's not the power amp, it's the preamp. I'm not quite sure how I got that wrong, but probably it's because I have to reach around awkwardly and blindly to hook up and unhook the amps.
Anyway it's the preamp; it has three (two-sided) 12AT7s. Before I spring for a new set, are there any other possible causes I should check? I mean aside from a regulator in the PS (which would affect both sides equally), there aren't any other active components, so I assume not, but still ... thanks and apologies for a stupid mistake.
Edits: 02/15/12
thanks, Tre' - strangely there is a small amount still there, but nothing like it was.
x
And see if noise follows. If so... you'll prolly need tube(s).
Try replacing the input tubes.
Tre'
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