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Tubes trouble?

Need help and advice.

Have an ARC PH5 Riaa where the tubes were changed two years ago. Sometimes when I play there is a humming sound that changes character when I put my hand on the cabinet and all of a sudden I am completely free of interference again. Where do I start? Guess it's a tubes that's bad. How do I find which one? Can I change just one tubes or do I have to change all of them? Is there any placement of the four that is less critical if a pipe is in worse condition? Thanks fore comments and tips. // Niklas

titus1
dill
2,525 posts
 

I would try some tubes shields for the 6922 tubes.

lewm
13,043 posts
 

Dill’s idea is not a bad one. A shield should both quell microphonics and shield from RF. (But the tubes in an ARC may already be shielded.) You might also check that the unit is well grounded. When you touch it, your body affords another path to ground. Sounds like microphonics though. All tubes are to some degree microphonic. You might try moving the tubes that are nearest to the phono inputs to the more distant position from the phono input and move those distant tubes close to the photo input; in other words swap them in pairs. This is assuming they’re all of one type, e.g., all 6922s or whatever.

newbee
4,767 posts
 

I doubt that this is a tube problem. My first guess would be that it is somewhere in the grounding or wires (IC's). Check to make sure all of your IC's are not near any transformers, etc and all connections are solid, especially grounds from your TT and phono stage.

ghdprentice
6,969 posts
 

I agree with @newbee it doesn’t sound like a tube problem, good advice on likely fixes.

 

But for all my ARC equipment I have an extra set of tubes. If a funny noise comes up in a single channel, I change the tubes in that channel (or both if I don’t know which is which. If in both channels then the 6550. If this doesn’t work I change all the tubes just to be absolutely sure it is not a tube problem. If at any time the problem goes away, I swap in the old until I find the little bugger.

If all tubes are fine it is something else. For me it never has been.

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