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[jeepy]

Hello,
Could the 2sa970 and 2sc2240 replace the MPSL01 and MPSL51 even if their Hfe is higher? ..>200. (I have a reasonable stock of those). Output stages will use IRF130 and power rails = +/-41V.
Thanks,
jeepy

 

[Zen Mod]

Hello,
Could the 2sa970 and 2sc2240 replace the MPSL01 and MPSL51 even if their Hfe is higher? ..>200. .....

irrelevant

look just at P , I , U of xsistors for substitution

....... Output stages will use IRF130 and power rails = +/-41V.
........

rails are somewhat high for those IRF's

be careful with that axe , Eugene ;

either :

- use lower rails,or
-use mosfets with higher voltage range,or
-be sure that you're not using full swing on output

 

[Uunderhill]

Hello,
Could the 2sa970 and 2sc2240 replace the MPSL01 and MPSL51 even if their Hfe is higher? ..>200.

Generally speaking, with an amp made from BJT's, its the circuit that sets the gain,
not the Beta (hFE) of the BJT.
But don't use a darlington where a singe BJT should be.

If you look at the datasheets, there are typically clues - like Noise Figure or maximizing hFE
of where its best to set the bias for that particular BJT.

As Zen pointed out, also make sure Vce(max) and P are well within the BJT's limits.

In this case, I'm wondering if the higher Beta will actually improve the CMRR
of the differential pair.
.

 

[jeepy]

Generally speaking, with an amp made from BJT's, its the circuit that sets the gain,
not the Beta (hFE) of the BJT.
But don't use a darlington where a singe BJT should be.

If you look at the datasheets, there are typically clues - like Noise Figure or maximizing hFE
of where its best to set the bias for that particular BJT.

As Zen pointed out, also make sure Vce(max) and P are well within the BJT's limits.

In this case, I'm wondering if the higher Beta will actually improve the CMRR
of the differential pair.
.

Thanks to you and Zen!
The 300mW PD may not be enough for the Vas and driver so I will use the 2N5551 instead. I will use the 2SA940 for the diff pair due to better noise figure and other specs in range.
Thanks again