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My Cary PH 302 phono amp MM hum?

My Cary tubed PH 302 phono amp sounds great running an Ortofon Rondo Blue through the Moving Coil section but it has developed a hum with my Shure V15 III in the MM input. I have experimented with all the usual suspects that can be related to ground loop feedback. So far nothing has worked. The tubes test perfect. I have the same hum with a variety of cartridges and turntables. Has anyone had this problem with this phono stage? Thanks.
Sharpe
sharpe

Showing 3 responses by mechans

mechans
3,048 posts
 
A SUT is a Step Up Transformer, typically used for low output MC cartridges.
mechans
3,048 posts
 
I imagine your Sylvania VT 229s would be a truly good tube for the phono amp as long as they were quiet. How do you like them this far.
mechans
3,048 posts
 
Sorry to reply so late. I was away. The tubes which frequently is still available as NOS in their military boxes thus NIB (new in Box) is a great choice but the price is daunting. I had thought the 6SL7s would cost less. It is a decent price for the more widely used 6SN7. Is this from a really good vendor? If so I might just hold my nose and accept the cost. They will last a long time and have (I hope) been properly screened and sort of matched. I add that "sort of" because it is really hard to find close matching in tubes that old and rare. I would ask the vendor to match as well as they can, but in your circuit it may not matter. Make sure they are returnable because you really do need quiet examples. Good luck.
Steve
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