[time-nuts] FTS 1200 transistor replacement
csteinmetz at yandex.com
Sat May 17 22:39:21 UTC 2014
>what transistor will have even lower noise than the than low noise BC 109.
Generally speaking, the baseband noise of a bipolar transistor is
most strongly influenced by the transistor's base spreading
resistance. Of course, the transistor also needs to have whatever
other characteristics are required in the application circuit -- in
particular, adequate current gain and transition frequency at the
operating point and sufficiently low input capacitance -- and these
may be mutually exclusive with lowest base spreading resistance.
The 2SD786 and MPSA18 may be good candidates. That said, I seriously
doubt you will get usefully better phase noise by using a "better"
transistor in this location.
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