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SPEAKER HUM

I have been playing with a new system. I was driving my speakers with a MingDa MC 34 AB tube amp (75 wt/ch ultralinear 40wt/ch triode) which is powered with 8 EL 34 tubes. It can be used as an integrated amp, and when I used it as such, it was DEAD quiet.
I decided to make a good thing better, and just got the matching MingDa MC 2A3X preamp to go with it. The speaker hum when both are powered up is awful...not that very low level stuff you sometimes get with an amp/preamp set up...but loud enough to hear during quiet passages of musical pieces.
I have been tormented in the past with trying to eliminate speaker hum...any help out there for this system??
Thanks so much
rsasso
rsasso OP
39 posts
 
To Tvad,

I dont have any of these 6SN7's to rotate right now. The microphonic tube you mentioned as common; is that normal as well? The microphonic effect of tapping the tube doesnt mean the tube is damaged, correct?
Post removed 
millicurie999
57 posts
 
As Swampwalker mentioned, amp and preamp in two different outlets can cause serious hum. Since you tried another preamp and it still gives you hum (albeit less), maybe it is indeed the ground loop introduced by different components in different power lines.

Can you borrow a power conditioner/surge protector and plug everything into one shared line?
rsasso OP
39 posts
 
To Tvad,

Thanks again for your very knowledgable input on my setup. It is appreciated, and I will get some 6SN7's and try out your suggestions.
rsasso OP
39 posts
 
To Millicurie999

Since the amp is about 10ft away from the preamp,it would take an extension cord, but yes, I can get everyting (sources included) into the same surge protector.

Out of curiosity though, if that is the problem, would a cheater plug on the amp (plugged into its own outlet as it is now) diagnose the problem...would I expect the hum to disappear if the separate outlet situation is causing the hum?
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