ok, i couldnt remember which NAD amp just used plain old 2955/3055 with none 
To be honest yes, the MJ21195/6 should be fine, even MJ15024/5 will be good
One thing NAD often do is use fixed resistors for bias. You may have to change that as the biasing will be different on the newer transistors. If there's a pot, then you're fine
To be honest yes, the MJ21195/6 should be fine, even MJ15024/5 will be good
One thing NAD often do is use fixed resistors for bias. You may have to change that as the biasing will be different on the newer transistors. If there's a pot, then you're fine
MJ15015 and 16 datasheet refers to the 3055-2955 spec. They have a higher Vceo and an actual SOA, not as big as 21195. I got my On Semi versions for $1.28 each from farnell (newark in USA). Depending on layout, you might have to put 10-20 pf across the B-E leads to prevent oscillation, especially on the MJ15016 which has ft of 4 mhz. The MJ15015 ft is .8 mhz.
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If there is no bias pot, you want something close to the original 3055/2955. MJ21195/6 would *work*, but the bias would need to be adjusted if possible. MJ15015/16 are much closer to the Moto/ON 3055 (only slightly larger die with the same layout and processing) so the bias should be closer to correct without adjustment. The extra 10-20 pF cap trick may be needed regardless of what type is used if they are not the originals.
or choose any you like but add a trimmer to the bias circuit and you know exactly what are you doing
done it a million times for both pioneer and kenwood amps that featured no trimers in the bias circuit ...
benefit of the above could be the possibility of beefing up the bias at a desirable level ( dont realy think that will make the NAD any better but just in case )
Off topic
at the time this was all of course carbon cheap resistors the tracking though and tollerance after 30-40 years of operation was unbelivable ...talk about excellent use of available parts at the time.... amazing japanese made products !!!
done it a million times for both pioneer and kenwood amps that featured no trimers in the bias circuit ...
benefit of the above could be the possibility of beefing up the bias at a desirable level ( dont realy think that will make the NAD any better but just in case )
Off topic
at the time this was all of course carbon cheap resistors the tracking though and tollerance after 30-40 years of operation was unbelivable ...talk about excellent use of available parts at the time.... amazing japanese made products !!!
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