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In Reply to: RE: Serious Micro-Phonics and Hum from Citation V posted by mr9iron on July 07, 2012 at 01:06:10
In my experience with generic tube amplifiers (not specific to the Cit V), those symptoms point to two possibilities. First, you may have lost the NFB connection. That will increase the gain tremendously and also increase hum. Second, the amplifier may be oscillating at a frequency above the audio range. That almost always creates microphonics and hum, and can also burn out tweeter voice coils.
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Buy Chinese. Bury freedom.
Follow Ups:
"Buy Chinese. Bury freedom" - agreed, keep buying Chinese, support Authoritarianism..
The NFB possibility,if the NFB was not connected wouldn't I hear that tremendous big boomy "wide" -sound as well? I have heard this amp with it disconnected, and it has a very noticeable "big" wide bass-y sound, I do not currently detect that. If the NFB was the problem, would I hear this? I will go through that loop to be sure..
Now your second idea is intriguing.."oscillating above the audio range" You said it can ruin a tweeter, would there be anything I could hear or detect, that would indicate it's killing my tweeter? I do not own a scope..
What would cause this oscillation and is there any way I can test for it?
I should mention I am not a "super tech" so a really involved explanation might go over my head :)
thanks for your reply,
Jeff
The tweeter comment was only intended as a general warning about using the amp in its present condition. Based on what you've said, I wouldn't power it on again without dummy loads and a 'scope. Anyway, if the NFB connections appear good, I think you'll need a more experienced hand to go in and troubleshoot. Not to state the obvious, but have you discussed this with Jim McShane? If he's not able to help over the phone, it would seem you only have a few alternatives. One would be to pack it up and send it to Jim for a look. The other would be to locate a local shop or vacuum tube afficionado who will look at it, preferably someone willing to consult with Jim while investigating the problem. Maybe if you put out a general distress call here on the tube forums, someone can recommend a resource in your area.
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Buy Chinese. Bury freedom.
Yes it may be in fact what I have to do. I do have a dialog with Jim, he's always willing to help. However I usually try to see if it's something simple by pining the forum first before contacting him, he's quite a busy guy and I don't like to hound him if it's something minor I can figure out. But yeah it looks like this could be involved and if we need to scope this amp out then I will probably do as you suggest.. Hate to admit defeat :)
thanks,
Jeff
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