Strange waving in speakers after tube replacement in amplifier

[halloleo]

One power tube of my 3-year old Neuhaus T-2 hifi amplifier is broken. So I ordered from thetubestore.com replacement tubes. However with the replacements I have strange troubles: When I switch the amp on I get in the speakers a strong slow movement of the membranes with a frequency of ca. 2Hz. I took a video for better demonstration:

 

 

(wait for the waving settling after a few seconds)

 

Music plays kind of fine on top of this, but I am worried to damage the speakers with this in the long term. This didn’t happen before. Any clue why this happens now and how I can prevent it? Might be other tubes from another seller do a better job? How can I know?

 

Many, many thanks!

[JW Audio]

It seems to be leaking DC current to the speakers. I would not play through that tube.

[JW Audio]

I would send this vid. to thetubestore and I'm sure they will replace the tube for you.

Good luck and keep us posted with what happens

[huyanep]

Right,Good luck and keep us posted with what happens

[speavler]

anyone else have issues with thetubestore? i've had so many issues with microphonics on tubes i've bought from them, i've resorted to ebay sources for nos and cryo'd tubes

[halloleo]

I would send this vid. to thetubestore and I'm sure they will replace the tube for you.

Good luck and keep us posted with what happens

 

Well, they say that their tubes themselves are not the problem. It is the fact that they do not match the amplifier (their tubes are "American" while the original tubes in the amp apparently where "Chinese") However thetubestore.com does not have these ones. :-(

 

I'm not sure what to do... Does anybody has experience with 6N7 tubes in the Neuhaus T-2 and what replacements I could use?

[zackthedog]

Well, they say that their tubes themselves are not the problem. It is the fact that they do not match the amplifier (their tubes are "American" while the original tubes in the amp apparently where "Chinese") However thetubestore.com does not have these ones. :-(

 

I'm not sure what to do... Does anybody has experience with 6N7 tubes in the Neuhaus T-2 and what replacements I could use?

 

It shouldn't make any difference if the tube is American or Chinese, if it's working properly. You probably got a tube with poorly matched sections, which is fairly common with American 6N7s.

 

You can get new Chinese 6n7s for $20 a pair on eBay, free shipping. The Russian ones are pretty well-made and sell for less than $2 a piece. At that price you could order 8 and make sure at least four of them won't give you any problems.

[zackthedog]

It occurred to me to ask: You posted a while back saying you needed to replace the 6N7s. Did you have a problem with the old tubes? I ask because it's possible something is wrong with the amp. Remind me again why you needed a new set of tubes?

[zackthedog]

Also, have you tried swapping the new tubes from one channel to the other? If the oscillation follows the tubes, then you know it's the tubes. If not, there may be a problem with the amp.

[Bob Stern]

Could be a bad electrolytic capacitor.

 

http://en.wikipedia.org/wiki/Motorboating_(electronics)

[halloleo]

... Remind me again why you needed a new set of tubes?

 

Well, one day when I switched on the amp a big cracking noise and flickering light came from one tube. I immediately switched the amp off and try maybe an hour or two later again - with the same result. That's why I thought I need to replace the tube.

 

And indeed with the new tube(s) I don't get any sign of "light and fire", but this very disconcerting waving of the speaker membranes...