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Mystery of the whistling amplifier

I replaced the manufacturer-supplied low-power tubes (two 12AU7 in the pre-amp section; four 12AT7 in the amp section) in my VTL integrated amp with NOS Telefunkens from Vintage Tube Services. After a few months I started hearing hissing and whistling through the speakers. It happens regardless of the source (DAC or the phono preamp).  I read here and elsewhere that this was probably caused by about-to-fail preamp tubes. Here're the things I've tried to address this:

1.   I took the 12AU7s out and switched them between their sockets. I also reseated them in their original positions. These measures made the problem go away for a while. Then it came back.

2.  I put the manufacturer-supplied tubes (JJ Elec ECC81) back in, and that "solved" the problem for a day or two; then it didn't.

3.  A Youtube video recommended scraping the pins shiny with an x-Acto knife blade. I did this, and it worked for a while. Doing it again, perhaps more thoroughly, also worked for a while, and seems to have reduced the overall level of the sound. I also hit the pins with Deoxit after scraping.

I listen to this setup several hours a day. Sometimes, like right now, there's no unwanted noise. When it is happening, you can't hear it through loud passages at all. But of course I want to fix this.

I'd welcome any suggestions or diagnoses before bringing this to the dealer.


john_g

Showing 1 response by john_g

john_g OP
80 posts
 
Thanks to all who responded. The problem is "solved." I tried yet another set of J&J tubes in the pre-amp section and still had hissing and popping. So I decided to take the thing back to the dealer, and replaced all six NOS Telefunkens (two 12AU7 in the pre-amp and four 12AT7 in the amp section) with the original J&J tubes the unit had been delivered with. Hissing and popping went away, and I now have six rather expensive tubes on the shelf.

In truth I noticed a subtle improvement in sound with the original tubes. Not sure what to make of all this but again I'm grateful for the help and suggestions here.
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