[dsavitsk]

I have a Melos SHA-1 with some Amperex 7308s. The tubes were NOS (from upscale) in January. About a month ago I started getting a high pitched squeal out of the right channel after the amp had been on for a few hours.* Changing the volume did not change the volume of the squeal which was just loud enough to be painful, even with the volume off. I found that flipping the input selector could get it to go away for a few minutes, but it would always return, and this didn't always work either.

To test if it was indeed the tubes, I swapped them to the opposite channels and the squeal went away completely. Now, a month later, it is back, but it is in the left channel now. Thus, it does seem to be following the tube, but it also seems that moving the tube (both switching channels as well as vibrating it through touching the input selector) gets it to go away for a bit.

So, has anyone had a similar problem, does this sound like a tube issue, or perhaps a biasing one, or something else? Are there any suggestions? Is this just the cost of NOS tubes in that I got a bad one?

-d


*If anyone searches, there is an old post from me about a squeal around my amp. This turns out to have been a laptop power supply that was plugged in nearby.

 

[go_vtec]

Based on your description, it mostly likely to be your tube. Just to be sure, when the squeal comes back, swap them and see if the noise is coming from the suspected tube. If so, you should replace it. Normally you may want to replace it with a matching pair to get consistent volume in both channel.

 

[gpalmer]

I believe what your describing is a microphonic tube...

 

[Chinchy]

I had issues that sounds just like the ones you were having with my Melos. I had a loud pitched hum on my left channel that was there intermittently, and if I used the input selector it would go away for a bit. Anyways, finally got to the point where I said, screw this, and sent it off to Carlo to be modded. He mentioned to me that part of his mods reroutes the left channel, which originally goes through the power supply section or something, and can cause problems. But then at the same time, when he was checking out my amp, he said that my tube sockets were corroded to the point where it was no longer acceptable. He swapped them out for new ones. Haven't gotten it back yet, so I can't guarantee if it fixed my issue or not, but you might want to get it checked out.

And if you want to get it modded by carlo, you can just PM him.

 

[pureofheart]

tubes!!!!! Had the same problem months ago and by replacing the tubes, the problem went away.
I recommend to get a cheap pair of tubes and give it a try. I am sure the problem will disappear.

Good luck. Melos is an excellent piece of machinery - when it works!