Canary Audio CA-606 tube pre-amp has a very high frequency squeel after warming up

Lee-Ross

New Member
Hey everyone, new to the forum, hoping somebody can help me out with some ideas.

The aforementioned pre-amplified that I have starts to emit a very high pitched squeeling noise after playing for about 15min. The frequency of the noise is fairly high, some people can hear it others can't. but I am able to record it on my iphone and amplify it for other to hear.

I sent it in to a local Tube gear builder/repair guy, for an unrelated issue,to be gone over and have any necessary repairs performed. He replaced the coupling capacitors in both channels with comparable Mundorfs.

Also replaced the 2 6DJ8/6922 tube with NOS Amperex Holland tubes. touched up some solders here and there cleaned contacts and selector switches.

This high frequency noise is still there. I've tried switching out the tubes with multiple different kinds. No luck.

Sidenotes:
-the frequency isn't constant, I can hear it changing pitch at idle with no signal going in.
-changing the input selector makes no difference
-noise gets louder as the volume knob is turned up.

Thanks,

Lee.
 
Welcome to AK.

Did it squeal prior to servicing? Clumsy installation of oversize caps can compromise stability by changing circuit layout and parasitic capacitances.
 
yes it did. The reason it first went in for service was mainly because the right channel was missing audio, and there was some the high frequency noise.
When it came back. audio was clear on both channels. but the noise was still very prevalent. And the guy who fixed it builds custom tube gear from scratch. So he's not a slop. And all the work looks ON POINT. to my eye at least.
Trouble is, being that he is about 50yrs old, he can't really here the noise. I don't think he can hear the frequency that the noise is at.
 
Inability to hear the noise isn't an excuse because test gear would easily reveal it. Just my worthless opinion, of course, but if this punter isn't properly equipped, then he shouldn't hang out a shingle. If you want the gang here to pontificate about possible causes for the noise, which they're always happy to do, then it would be helpful to post or link to circuit details. PDFs are best for posting complex drawings.
 
A scope would show it pretty easily even if the ears will not.

Sounds like its oscillating for some reason. Wild guess, maybe one of the filter caps is giving up and you're getting some weird interaction between the amp stages but it could be a whole lot of things really.
 
I would try moving the preamp to a different outlet, or different room and see if the noise is still present.
 
We could go on for a long time on what it could be.

What you need to do is contact the tech and let him know about the problem. Keep it polite and to the point. Don't start making assumptions, just let him figure it out.

The main point is keep communication open, polite and too the issue. The end goal is to get your stereo working and for him to keep a happy client.
 
Where are you located? There are five shops in the St. Louis area that can check this properly, and many others regionally.
 
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