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Old 3rd October 2011, 02:11 PM   #1
Mielke is offline Mielke  Germany
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Default Preamp input tube noise

Hello,
I wonder what different level pentode tube noise is to be expected from a pre with oldstyle octal input tubes like EF37, 6J7, WE 348A in comparison with newer noval tubes like EF804S or EF184. Are the newer tubes that quiter than the old ones and does that lead to a nearly noise free preamp or is the difference not that big?
Old tube have better tone qualities but I dont want them to be noisy in the quit passages of the LP record. So do I have to go with the new types?
Thanks, Mielke
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Old 3rd October 2011, 07:56 PM   #2
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As a rule, pentodes are noisier than triodes because of partition noise. For this reason, triodes are the most popular type of tube for use in an RIAA preamps.

Having said that, the noise sources in vacuum tubes is not generally well understood which means that many triode designs are noisier than they could be. This means it could be possible to design a pentode based RIAA preamp that is in fact quieter than many current triode designs.

To return to your original question, there are two major sources of noise at audio frequencies in vacuum tubes - shot noise and flicker noise. Of the two, flicker noise is generally the more serious and is mostly due to imperfections in the manufacture of the cathode. This means it can vary enormously between different samples of tubes of the same type but it also means that the quietest tubes will be obtained from the best manufacturers i.e. those who control their manufacturing processes the best. Since the art of vacuum tube making has arguably been mainly lost it is likely that samples of old types of tubes will be quieter than samples of their modern equivalents.

Cheers

Ian
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Old 3rd October 2011, 08:11 PM   #3
DF96 is offline DF96  England
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EF37A (not EF37) is supposed to be good. Miniature alternatives are EF86 or 6BR7. As Ian says, older ones (e.g. NOS) are likely to be better than recent manufacture.
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