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In the Forum: Analog Playback
In the Thread: 7788 tube mic pre design
Post Subject: The trouble with tubes...Posted by Paul S on: 1/13/2008
Why do we even bother with tubes for low levels?  Of tubes generally, I have used 6SN7s, 2A3s and EL34s with no known-to-me problems, but lots of various noise trouble with certain tubes, including 6DJ8 family, KT88s, and on and on, especially annoying in cases where I like other things about the tubes.  I have found quiet 6DJ8 tubes, but I have to go way out of my way for them.

One thing I have noticed, though, is that some problem tubes quiet down when operating points are lowered, where this is an option.  Of course, not all tubes are mechanically quiet, and most were not designed to be, either.  I use the old dark plastic (PETA, or something like that) Herbies dampers on tubes that are SUPPOSED TO BE quiet.

Jim, I know it's a stupid question, but how many 7788s have you tried, and from how many sources?  Haven't we all gotten/tried several bad tubes in a row at some point?

I don't know the 7788, but I am generally suspicious of too much gain from too low level, which is one reason why I prefer to jump start with a transformer.

I know you will find a solution!

Best regards,
Paul S

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