Siemens BS101, if you are referring to the output source follower mosfets. I have replaced
them quite successfully with IRF840 or IRF740 hexfets. The JFETs in the input stage cascode
are quite a different animal. Although I've specialised in Moscodes for 20+ years, I've never
had need to replace any, so I've never bothered to ask George Kaye to properly identify
them(orig. house numbered). But, given the circuit parameters, it can definitely be replaced
by 2SK117, 2SK170 or 2N3819. I've never seen either the BS101 or the jfet go noisey, so I
suspect chilling them may actually be chilling an adjacent resistor.

--
Stephen Sank, Owner & Ribbon Mic Restorer
Talking Dog Transducer Company
http://stephensank.com
5517 Carmelita Drive N.E.
Albuquerque, New Mexico [87111]
505-332-0336
Auth. Nakamichi & McIntosh servicer
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"Bob" wrote in message
nk.net...
The number on the old fet is 101, in the NTE/ECG listings this part is OEM
which means "good luck". The Super-It is a tube preamp with about 4 of
these fets. Background noise has gone up rapidly in past few months. When
these are cooled the noise stops until they warm up again then the noise
starts again.